Cat A vs Cat C Porting Australia Explained: Simple vs Complex Ports (2026)

Cat A and Cat C are the two number porting categories used in Australia, and which one applies to your port determines whether you wait 1 to 5 business days or 5 to 15-plus. This guide explains exactly what each category means, how your port category is determined under ACMA's Telecommunications Numbering Plan, and what happens differently at each stage of the process. By the end you will know which category your port almost certainly falls into, what realistic timeline to plan around, and what to do if things go sideways. For a full step-by-step walkthrough of the actual porting process, see our complete Australian number porting guide.

Quick Summary: Cat A vs Cat C at a Glance

What Is Category A Porting?

Category A is the simple port. It covers the most common scenario an Australian small business will encounter: a single geographic number or mobile number moving between two providers that use compatible underlying network technology. If you have an 02, 03, 07, or 08 prefix number and you are moving to a VOIP provider, there is a good chance you are in Cat A.The Category A process uses the Local Number Portability (LNP) system, which is the automated carrier-to-carrier infrastructure that handles the bulk of Australian number ports. When your new provider submits a Cat A porting authority, the LNP system validates your account details against the losing carrier's billing records, schedules the cutover, and flips the number at the agreed time. The technical cutover itself takes minutes. The 1 to 5 business day window is almost entirely waiting time for validation and scheduling, not technical complexity.What makes a port Category A comes down to three things. First, it involves a single number, not a block of numbers. Second, the number type does not require special handling, meaning it is a standard geographic or mobile number, not an ISDN service or a multi-line group. Third, the port does not cross a fundamental technology boundary in a way that requires manual carrier coordination. Most VOIP-to-VOIP ports and most ISP ATA-to-VOIP ports for geographic numbers fall into Cat A.

Category A Timeline: What Actually Happens

Day 1: Your new provider submits the porting authority form to the LNP system on your behalf. The losing carrier receives a notification.Days 1 to 2: The losing carrier validates the submitted account details against their billing records. If the account holder name, service address, and account identifier all match exactly, the port request is accepted. If anything does not match, it is rejected at this stage and the clock resets.Days 2 to 4: Cutover is scheduled. You or your provider nominates a preferred date and time window, typically during business hours. Most providers offer morning or afternoon windows. The cutover is booked.Cutover day: During the nominated window, your number flips from the old system to the new one. The technical change takes 15 to 60 minutes. During this window, call routing is in transition. Schedule your cutover during your lowest call volume period.After cutover: Your number is live on the new VOIP system. Test an inbound call immediately. If it lands on your new system, the port is complete. Your old service can now be cancelled. Not before.

What Is Category C Porting?

Category C is the complex port. It applies when the port involves circumstances that cannot be handled entirely through the automated LNP system. Category C ports require additional manual coordination between carriers, and sometimes between multiple carriers, which is why the timeline is longer and less predictable.Cat C is not rare, but it is less common than Cat A for typical small business migrations. The scenarios that trigger Category C are specific, and it is worth knowing them before you assume your port is straightforward.

What Triggers Category C

Technology crossover is the most common Cat C trigger for Australian businesses. If your current service is on a legacy ISDN circuit (ISDN2 or ISDN10/20/30), moving that number to a VOIP service crosses a technology boundary that requires manual decommissioning on the losing carrier's side. ISDN services cannot simply flip via the LNP system. They require the losing carrier to physically or logically decommission the ISDN service as part of the port. The PSTN copper shutdown that completed in 2025 has put many Australian businesses into this situation.Multi-number porting is another common Cat C scenario. If you want to port a range of geographic numbers together, rather than one at a time, the port is categorised as complex. This applies to businesses that have multiple geographic numbers on the same account and want them all to move to the new system simultaneously. Your provider can port them individually as Cat A ports over multiple requests, or as a grouped Cat C port. There are operational reasons to prefer one approach over the other depending on your cutover strategy.Multi-carrier services add complexity because the losing carrier cannot act alone. If your current phone service involves a wholesale arrangement where one carrier provides the underlying infrastructure and another provides the retail service, both carriers need to coordinate the release of the number. Your new provider may not have direct relationships with both parties. Manual coordination is required.Number blocks are always Cat C. If you are porting a consecutive block of geographic numbers (for example, a range of 10 numbers used by a small call centre), the port cannot be processed individually through the LNP system. It requires a Category C process with explicit block-level coordination.Certain legacy service types on obsolete infrastructure also trigger Category C. If your current service has an unusual technical configuration from years of accumulated changes, such as a number that has moved between carriers multiple times and has legacy routing flags in the system, your new provider may flag it as Cat C based on what they find when they look up the number. This is less common but it happens.

Category C Timeline: What Actually Happens

The Category C process follows the same general steps as Cat A, but with additional coordination stages that cannot be rushed. The gaining carrier submits the porting authority. The losing carrier acknowledges receipt. For Cat C, the losing carrier then needs to perform additional steps: de-provisioning ISDN equipment, coordinating with wholesale partners, or processing block-level changes. These steps require human scheduling, not just automated validation.Realistic Cat C timeline: 5 to 10 business days for a clean first-attempt port. The 15 business day upper end accounts for situations where the losing carrier's provisioning team has a queue, public holidays extend the window, or a minor coordination issue requires one back-and-forth before the cutover can be scheduled.Cat C rejection recovery takes longer too. If a Cat C port is rejected for a documentation reason, the resubmission and reprocessing adds 5 to 10 business days, not 3 to 7. This is why planning buffer time is even more critical for Cat C ports.

1300 and 1800 Numbers: A Separate Category

1300 and 1800 numbers do not use the Cat A or Cat C porting framework at all. They are non-geographic numbers managed under the ACMA's Smart Numbers database and delivered via a carrier assignment model rather than a network porting model. The process of moving a 1300 or 1800 number to a new carrier is technically a carrier assignment transfer, not a port.In practical terms for businesses: the process takes longer and involves different documentation. You will need to provide your Smart Numbers account details and, in most cases, sign a Right of Use (ROU) transfer document. Some providers manage this entire process on your behalf. Others hand you the forms. Confirm which approach your provider takes before you start.Timeline for 1300 and 1800 transfers: 5 to 15 business days for a straightforward transfer, up to 20 business days if documentation goes back and forth. Plan for 3 to 4 weeks from decision to go-live if your inbound 1300 number is a critical business asset. For full detail on how 1300 numbers work and what they cost, see our 1300 number guide.

How to Find Out Which Category Your Port Is

You do not have to guess. Your new provider can look up your number in the LNP database before you submit anything and tell you which category applies. This lookup is part of standard onboarding for any competent VOIP provider. Ask for it explicitly if they do not volunteer the information.The lookup tells the provider what type of service your number is currently on, which carrier holds the number, and whether any flags in the system indicate complex coordination will be required. From this information, they can categorise the port and give you a realistic timeline. If they say 'we will not know until we submit', push back. They should be able to give you a category assessment before submission.There are also clues you can use to anticipate the category yourself before you speak to a provider. If you have a single geographic number that has been on a standard business VOIP or NBN phone service for the past few years, you are almost certainly Cat A. If your service dates back to a period before NBN, if you were ever on an ISDN circuit, if you have multiple numbers on one account, or if you have changed providers multiple times and are unsure of what sits behind your service, Cat C is more likely.

Questions to Ask Your Provider to Determine Category

Ask your new provider these specific questions before submitting a porting authority form:Have you looked up my number in the LNP database? What does it show as the current service type? Is this a Category A or Category C port based on that lookup? What is your realistic timeline for this specific port, not the general range? If this is Category C, what is the reason and which carriers are involved? Have you done this type of port before, and what is your typical success rate on first attempt?A provider who answers these questions specifically and confidently has done this before. A provider who gives vague answers or says they need to submit first to find out is telling you something about their process. For a broader view of what switching to VOIP involves, see our VOIP vs traditional phone guide.

The ACMA Numbering Plan: What the Rules Actually Say

Both Cat A and Cat C porting are governed by the ACMA Telecommunications Numbering Plan. The Plan sets the regulatory framework for number portability in Australia: it establishes the obligation on carriers to support valid porting requests, sets the timeframes within which losing carriers must process ports, and defines what constitutes a valid rejection reason.Under the Numbering Plan, losing carriers cannot refuse a valid porting request because they want to retain your business. They are required to process valid requests within the prescribed timeframe for the category. For Cat A, the losing carrier must acknowledge and validate the request within 2 business days. For Cat C, the timeframe is extended to accommodate the additional coordination steps involved.The Plan also sets out the legitimate reasons a losing carrier can reject a porting request. These are technical and administrative in nature: account holder details do not match, the service identifier is incorrect, the number is not on the nominated account, or the account has an outstanding balance. A losing carrier cannot reject a port because 'the customer is still in contract'. An early termination fee may be charged, but it cannot block the port.The Communications Alliance administers the operational procedures under the Numbering Plan, including the Local Number Portability Code that sets out how the LNP system is used in practice. Your provider operates under this Code. If a provider is not following these procedures, that is a regulatory issue, not just a customer service issue.If a losing carrier is obstructing a valid port, the escalation path is: first, a formal complaint to the losing carrier's complaints team. Second, if that does not resolve within a reasonable timeframe, a complaint to the Telecommunications Industry Ombudsman (TIO). A TIO complaint reference triggers the carrier's internal escalation process and most obstruction issues resolve within days. The TIO service is free for consumers and small businesses. More detail on rejection handling is in our number porting timeline guide.

How Category Affects Rejection Handling

Port rejections work the same way for Cat A and Cat C: the losing carrier returns a reason code, your new provider communicates this to you, you correct the information, and the port is resubmitted. The difference is what the rejection costs you in time.A Cat A rejection that is corrected and resubmitted on the same day adds 3 to 7 business days to your timeline. The port restarts from the beginning. If your original timeline was 3 days and you receive a rejection on day 2, you are now looking at 5 to 10 business days total from submission.A Cat C rejection adds 5 to 10 business days per rejection cycle. This is because the resubmission restarts the manual coordination process. If your losing carrier's provisioning team has a queue for Cat C processing, you re-enter that queue from the bottom. Two rejections on a Cat C port can stretch the total timeline past 4 weeks.The most common rejection reason for both categories is an account holder name mismatch. The name submitted on the porting authority must match the account holder name exactly as it appears in the losing carrier's billing system. A single character difference, a maiden name versus married name, a trading name versus legal entity name, or a company name with 'Pty Ltd' where the system has 'Pty. Ltd.' is enough to trigger a rejection. Verify the exact name before submitting.For Cat C ports specifically, there is an additional rejection scenario that does not apply to Cat A: coordination failure. This is where the losing carrier begins the decommissioning or coordination process and encounters a technical complication with the legacy infrastructure. This is relatively rare but it is specific to Cat C. Your provider should communicate clearly if this is the reason for a delay and what steps are being taken to resolve it.

Planning Your Timeline Based on Category

The correct approach is to work backwards from your target go-live date, not forwards from your decision date. Most businesses do it the wrong way.For a Category A port: start by confirming the category with your provider. Add 5 business days for the port timeline. Add 7 business days buffer for one potential rejection. Add 10 business days to set up and test your new VOIP system on a temporary number before the port completes. Total minimum lead time from starting the process to a safe go-live date: 4 weeks, including buffer.For a Category C port: the same structure applies but the numbers are larger. Add 15 business days for the port timeline. Add 10 business days buffer for one rejection cycle. Add 10 business days for system setup and testing. Total minimum lead time for a safe Cat C go-live: 6 to 7 weeks. Businesses in ISDN-to-VOIP migrations who have hard go-live deadlines should start the process 8 weeks out.Your new VOIP system should be fully configured and tested on a temporary number before you submit the porting authority. When the port completes, the number lands on an already-working system. This is not optional. Businesses that submit the port and then start configuring the system create a scenario where the port completes before they are ready. For a full view of the migration process, see our landline to VOIP migration guide.

Australian Businesses: What to Know Before You Start

The porting category question has become more relevant for Australian businesses since the PSTN copper shutdown completed in 2025. If your business was on a traditional copper-based landline at any point in the past decade, your service has either already been migrated to an NBN-based VOIP service by your ISP, or you are overdue for the transition.The NBN migration created a specific situation that catches businesses by surprise. When the NBN was rolled out, ISPs moved customers from PSTN to VOIP via the ATA port on the NBN-supplied modem. This happened quietly, with minimal explanation to customers. The result is that many Australian businesses today have a VOIP number delivered via an ISP ATA, without knowing it. Their phone plugs into the green port on the router. They have no SIP credentials. They have no way to add features or port the number independently.For this cohort, porting to a proper VOIP provider is almost always a Category A port. The number is a standard geographic number on a standard NBN-based VOIP service. The complexity is the account detail verification, not the technology. Your provider will confirm this when they look up the number.The businesses more likely to be in Category C are those that have been operating on legacy infrastructure for an extended period. ISDN services were common in Australian businesses throughout the 2000s and early 2010s. If your business dates from that era and has never done a significant phone infrastructure review, there is a real chance your service has ISDN components. Ask your current provider what type of service your number is on before you engage a new provider. 'We are on NBN' is a sufficient answer for most modern services. 'We are on ISDN' or 'we have a T-series circuit' means you are in Cat C territory.

What Most Businesses Get Wrong About Porting Categories

Mistake 1: Assuming Category A and Getting Surprised by Category C

The most expensive mistake in porting planning is assuming your port is Category A without confirming it, then building a go-live plan around a 1 to 5 day timeline. If your number turns out to be Cat C, your 5-day plan becomes a 15-day minimum. Businesses that have announced a go-live date to staff and customers and committed to a system launch date cannot easily absorb a 10-day slip. The fix is 5 minutes at the start of the process: ask your provider to confirm the category before you plan anything around a timeline.

Mistake 2: Not Verifying the Exact Account Holder Name Before Submitting

Account holder name mismatch is the leading rejection reason for both Cat A and Cat C ports. It is also entirely preventable. The fix is a 5-minute call to your current provider before submitting anything: ask them to read out exactly what appears as the account holder name in their system. Write it down character for character. If the account was set up under a former business name, a previous owner's personal name, or a legal entity name that differs from your trading name, the porting authority must use the name in the system, not the name you go by. Submit what the system has.

Mistake 3: Treating 1300 and 1800 Numbers as Standard Ports

1300 and 1800 numbers are not ported through the Cat A or Cat C LNP framework. They are transferred through the ACMA Smart Numbers database via a carrier assignment process. This distinction matters because the timeline is different (5 to 20 business days, not 1 to 5), the documentation is different (Right of Use transfer, not a standard porting authority), and the process is different (carrier assignment versus LNP submission). Businesses that treat a 1300 number like a standard geographic port will submit the wrong forms and add weeks to their timeline. If you have a 1300 or 1800 number, confirm explicitly with your provider that they understand it goes through the Smart Numbers process, not the standard porting system.

Your Next Steps: Category Confirmation Checklist

Before submitting any porting authority, work through this checklist:[ ] Ask your new provider to look up your number in the LNP database. Get a written confirmation of whether it is Cat A or Cat C. [ ] If Cat C: ask your provider to confirm which specific factor is triggering the Cat C categorisation (ISDN, multi-number, multi-carrier, etc.) and what coordination is required. [ ] If you have a 1300 or 1800 number: confirm with your provider that they are using the Smart Numbers process, not the LNP porting framework. Get a realistic timeline in writing. [ ] Call your current provider and ask them to read out the exact account holder name as it appears in their system. Write it down. This is what goes on the porting authority form. [ ] Confirm the service identifier (SPIN or account number at the service level) for the specific number you are porting. [ ] Set your go-live date based on the confirmed category: 4 weeks minimum for Cat A, 6 to 7 weeks for Cat C, 4 weeks for 1300/1800 transfer. [ ] Set up your new VOIP system on a temporary number. Configure call routing, IVR, ring groups, voicemail. Test inbound and outbound calls. Do not submit the port until the system is ready. [ ] Choose a cutover date and time window during your lowest call volume period. [ ] Forward calls to a mobile number during the cutover window as a backup. [ ] Brief your team on the cutover date and what to expect. [ ] After the port completes and you have tested inbound calls successfully: cancel your old service.If you want guidance on which provider handles your specific porting scenario smoothly, our team can recommend based on your number type, current setup, and business size. Visit the Get a Recommendation page and tell us what you are working with.

What is Cat A porting in Australia?

Cat A (Category A) is the simple port category under the ACMA Telecommunications Numbering Plan. It applies to individual geographic numbers (02, 03, 07, 08 prefix) and mobile numbers moving between providers using compatible network technology. Cat A ports are processed through the automated Local Number Portability (LNP) system and typically take 1 to 5 business days. Most Australian small business VOIP migrations are Category A ports.

What is Cat C porting in Australia?

Cat C (Category C) is the complex port category. It applies when the port involves a technology crossover (such as moving from an ISDN service to VOIP), when multiple numbers are being ported together in a block, when multiple carriers are involved in delivering the current service, or when legacy infrastructure requires manual coordination on the losing carrier's side. Cat C ports require additional manual steps beyond the automated LNP system and typically take 5 to 15 business days.

How do I find out if my port is Category A or Category C?

Ask your new provider to look up your number in the LNP database before you submit a porting authority. A competent provider can tell you the current service type on your number and categorise the port based on that information. You do not have to submit anything to find out. If the provider says they cannot tell you the category until after submission, ask why. Most modern VOIP providers can give you a category assessment within minutes of looking up the number.

Does porting from an ISP green port (ATA) count as Cat A or Cat C?

Porting a number from an ISP ATA service to a proper VOIP provider is typically Category A. The number itself is a standard geographic number, and the fact that it is currently delivered via an ISP-controlled ATA on an NBN modem does not change the port category. The category is based on the carrier-level service type, not the endpoint hardware. Your new provider can confirm this when they look up your number. The process is the same as any Cat A port: porting authority form, account detail verification, LNP submission, cutover scheduling.

Is porting a 1300 number Cat A or Cat C?

Neither. 1300 and 1800 numbers are not ported through the Cat A or Cat C LNP framework at all. They are non-geographic numbers managed in the ACMA Smart Numbers database under a carrier assignment model. Moving a 1300 or 1800 number to a new carrier is a carrier assignment transfer, not a port in the technical sense. The process requires different documentation (Right of Use transfer) and takes 5 to 20 business days. If your provider treats a 1300 number as a standard port, they are using the wrong process.

What makes a port become Category C instead of Category A?

The factors that trigger Category C are: the service is on an ISDN circuit (ISDN2 or ISDN10/20/30) rather than a standard NBN VOIP or PSTN line; you are porting multiple numbers together as a block rather than individually; more than one carrier is involved in delivering your current service and both need to coordinate the release; or the number has legacy routing flags in the system that require manual resolution. Your provider can identify these factors by looking up the number before submission. Most single-number NBN VOIP ports are Cat A.

How long does a Cat C port take in Australia?

Category C ports typically take 5 to 15 business days for a clean first-attempt port. In practice, many Cat C ports complete in 7 to 10 business days. The upper end of 15 business days applies when losing carrier provisioning queues are full, public holidays extend the window, or a minor coordination issue requires one back-and-forth. A Cat C rejection adds 5 to 10 business days per cycle. For planning purposes, allow 6 to 7 weeks from starting the process to a safe go-live date, including setup time and one rejection buffer.

Can my current provider refuse to do a Cat C port?

No. Under the ACMA Telecommunications Numbering Plan, losing carriers are legally required to support valid porting requests regardless of category. A provider can reject a port for legitimate technical reasons such as account detail mismatches, but they cannot refuse to process a valid Cat C port because the coordination is inconvenient or because they want to retain your business. If a losing carrier is obstructing a valid Cat C port, the escalation path is: formal complaint to the losing carrier's complaints team, then a complaint to the Telecommunications Industry Ombudsman (TIO) at tio.com.au if that does not resolve it. Most obstruction issues resolve quickly once a TIO reference is in play.

What is the ACMA Numbering Plan and how does it relate to porting categories?

The ACMA Telecommunications Numbering Plan is the regulatory framework that governs how phone numbers are allocated, managed, and ported in Australia. It establishes the obligation on all carriers to support number portability, sets the timeframes within which losing carriers must process ports by category, and defines valid rejection reasons. The Communications Alliance administers the operational procedures under the Plan, including the Local Number Portability Code that governs how the LNP system works in practice. When providers refer to Cat A and Cat C, they are using categories defined by this framework. The ACMA website at acma.gov.au has the full Numbering Plan for reference.

I am moving from a traditional ISDN service to VOIP. Is that Cat C?

Yes. Moving from an ISDN service (ISDN2, ISDN10, ISDN20, or ISDN30) to a VOIP provider is a Category C port. ISDN services cross a technology boundary that cannot be handled through the automated LNP system. The losing carrier needs to decommission the ISDN equipment and release the number through a manual coordination process. Since the PSTN copper shutdown completed in 2025, ISDN-to-VOIP migrations have become the most common Cat C scenario for Australian businesses. Allow 6 to 7 weeks from decision to go-live and confirm your new provider has experience with this specific migration type.

What happens to my calls during a port cutover window?

During the cutover window, which is typically 15 to 60 minutes for Cat A and 1 to 4 hours for Cat C, calls to your number may not connect reliably. Some calls will route to the old system, some to the new, and some may receive a temporary 'number not available' message. This is normal propagation behaviour and is not a sign that the port has failed. Manage it by scheduling the cutover during your lowest call volume period (early morning or late afternoon), forwarding your number to a mobile before the window starts as a backup, and testing an inbound call as soon as your provider confirms completion. Once the test call lands on your new system, the cutover is done.

Related reading:

• number porting guide
• porting timelines