If your new phone shows 'Not Registered', 'No Service', or a blank line display: this is normal. The phone is waiting for SIP credentials from a VOIP provider. This guide explains exactly what that means and how to fix it.
Related guides: What is VOIP? A plain English guide for Australian businesses -- Best VOIP phone system for small business Australia -- Best SIP desk phones available in Australia -- ATA adapter guide: keeping analogue phones on VOIP -- QoS and SIP ALG settings on Australian routers
Why Your New IP Phone Shows 'Not Registered'
An IP desk phone is a terminal device -- the equivalent of a screen without a computer behind it. To make and receive calls, it needs to connect to a VOIP service using SIP (Session Initiation Protocol). The SIP service is provided by a VOIP carrier: a company that gives you a phone number, routes your calls, and provides two authentication credentials (a SIP username and SIP password).
Until those credentials are entered, the phone has nothing to register with. 'Not Registered' is the phone's way of saying: I am ready, but I do not know who my VOIP provider is.
The NBN Phone Port: Why It Does Not Work With an IP Phone
Many businesses assume a new IP phone will plug into the phone port on the back of their NBN modem (typically the green port). It will not -- and understanding why saves significant time and frustration.
The green phone port on your NBN modem (an ISP-controlled ATA output) is an analogue FXS output. It is connected to your ISP's own built-in VOIP service and is designed for traditional analogue handsets (Panasonic, Uniden, etc.) only. An IP phone connects to your router via Ethernet and communicates directly with your VOIP provider using SIP. The two paths are completely different -- an IP phone cannot use the ISP's phone port under any circumstances.
If your business has been using the green port with a standard cordless phone, that service is ISP-controlled. The SIP credentials are locked inside the modem firmware. You cannot retrieve or reuse them with an IP phone. To use an IP desk phone, you need a separate VOIP account with credentials you control.
What You Actually Need
Before you can make a call, you need four things:
1. A VOIP provider account. This is the service that gives you a phone number and routes your calls. Signing up typically takes 10-15 minutes online.
2. SIP credentials. Your provider gives you a SIP server address, SIP username, and SIP password. These go into the phone's configuration.
3. An Ethernet connection. Your IP phone connects to your router or network switch via an RJ45 cable -- the same type used by computers. Do not plug it into the green phone port.
4. Power. Either a standard power adapter (usually supplied with the phone) or a PoE (Power over Ethernet) switch, which delivers power through the network cable.
Step 1 -- Choose a VOIP Provider
Your VOIP provider is the company that handles your calls and issues the SIP credentials your phone needs. When evaluating AU providers, look for:
Month-to-month terms. Avoid lock-in contracts until you have confirmed the service suits your setup. Most reputable AU providers offer no-contract plans.
Auto-provisioning support for your phone brand. Some providers support automatic configuration of Yealink and Grandstream phones -- the phone contacts the provider's server on first boot and downloads its own settings, no manual entry required. This is the easiest path if your provider supports it.
Transparent per-second or per-minute call rates. Look for clear AU pricing on the provider's website. Per-call flat rates penalise short calls; per-second billing is fairer for most business calling patterns.
Local number included. Confirm the provider can issue or port a number with your local area code, or a 1300 number if that is what your business needs.
Step 2 -- Get Your SIP Credentials
After signing up, your provider will issue SIP credentials. These are typically provided via email or a self-service portal and consist of three items:
SIP Server / Proxy: the provider's SIP server address (for example, sip.yourprovider.com.au or a numeric IP address).
SIP Username / Extension: your account identifier or extension number.
SIP Password: the authentication password for your SIP account.
Store your SIP credentials in a password manager, not only in the phone. If the phone is factory-reset, replaced, or stolen, you will need these to reconfigure it. SIP passwords should be treated the same as email account passwords.
Step 3 -- Connect Your Phone to Your Network
IP phones connect via Ethernet (RJ45). Most phones include a secondary Ethernet port (labelled PC) that passes network connectivity through to a connected computer, so a single cable run can serve both the phone and a desktop PC.
Connection options:
Direct to router: Simplest setup for one or two phones. Run an Ethernet cable from the phone's WAN or LAN port to any available port on your router.
Via a network switch: For offices with multiple devices. Connect the phone to the switch the same as any other device.
PoE (Power over Ethernet): If your switch supports 802.3af PoE, the phone can draw power through the Ethernet cable. No separate power adapter needed.
Wi-Fi: Mid-range and high-end IP phones typically support 802.11n or 802.11ac Wi-Fi. Wired Ethernet is always preferable for call quality and registration stability. Use Wi-Fi only where cabling is not practical.
Do not connect your IP phone to the green phone port on your NBN modem. That port outputs an analogue signal and is physically incompatible with Ethernet. Your phone should connect to a standard Ethernet LAN port on your router or switch -- typically grey, yellow, or black coloured, and labelled LAN.
Step 4 -- Configure SIP Credentials
Option A: Auto-Provisioning (Easiest)
Some VOIP providers support auto-provisioning for Yealink and Grandstream phones. When you connect the phone to your network, it contacts the provider's provisioning server and downloads its configuration automatically. No manual credential entry required.
To check if your provider supports this, look for 'auto-provisioning', 'zero-touch provisioning', or 'plug and play' on their website or sign-up portal. You may need to register your phone's MAC address (printed on the underside of the phone) in your provider's account portal first. Once registered, power the phone on and it should configure itself within a few minutes.
Option B: Manual SIP Configuration via Web Interface
If your provider does not support auto-provisioning, enter SIP credentials manually through the phone's web interface:
1. Find your phone's IP address. On most Yealink phones: press OK, then navigate to Status > Network. On Grandstream phones: press the Menu button and navigate to Status > Network Status.
2. Open your phone's admin page. On a computer connected to the same network, open a browser and type the phone's IP address into the address bar. Log in with the default admin credentials (Yealink: admin/admin; Grandstream: admin/admin, or admin followed by the last 6 characters of the MAC address for some models).
3. Navigate to the SIP account settings. Yealink: Account > Account 1. Grandstream: Accounts > Account 1.
4. Enter your SIP credentials. Fill in the SIP Server, SIP Username (or Auth Username if prompted separately), and SIP Password fields exactly as provided by your VOIP provider.
5. Save and confirm registration. After saving, the phone will attempt to register. The display should show your phone number or extension within 10 to 30 seconds if credentials are correct.
Step 5 -- Make a Test Call
Once the phone shows registered, confirm it is working correctly:
Outbound call: Dial your mobile number from the IP phone. Confirm the call connects and audio is clear in both directions.
Inbound call: Call the IP phone from your mobile. Confirm it rings and that you can answer.
Voicemail: Let a call go to voicemail to confirm the voicemail greeting is configured and messages can be retrieved.
If all three work, setup is complete.
Troubleshooting: Phone Still Shows 'Not Registered'
Check Your SIP Credentials First
The most common cause of registration failure is a credential typo. SIP passwords are case-sensitive. Re-enter the SIP server address, username, and password carefully. If your provider's portal shows a different format for the SIP server (e.g., with or without sip: prefix), try both. Confirm with your provider that the account is active and the credentials are correct before proceeding.
Disable SIP ALG on Your Router
SIP ALG (Application Layer Gateway) is a router feature that attempts to manage SIP traffic. On most Australian consumer routers and NBN gateways, it is enabled by default and frequently corrupts SIP signalling, preventing phones from registering.
SIP ALG is the most common cause of IP phone registration failures in Australian home and small business setups. Log into your router's admin interface and disable it. Look under Advanced, NAT, or Firewall settings. See our guide to QoS and SIP settings on Australian routers for step-by-step instructions by router brand.
Check Your Firewall
SIP requires outbound access on UDP port 5060 (SIP signalling) and UDP ports in the range 10000 to 20000 (RTP audio). If your office is behind a managed firewall -- common in commercial buildings with shared IT infrastructure -- these ports may be blocked. Check with your IT administrator or building manager.
Check Your Internet Connection
A highly variable or unstable internet connection can cause intermittent registration drops. Run a speed test and ping test from the same network. Each simultaneous VOIP call requires approximately 100kbps of symmetrical bandwidth. For most businesses on NBN 25 or above, bandwidth is not the issue -- latency stability is. If your ping varies significantly (high jitter), contact your ISP or look at your router's QoS settings to prioritise VOIP traffic.
Factory Reset as a Last Resort
If credentials are confirmed correct and SIP ALG is disabled but the phone still will not register, a factory reset and fresh configuration is sometimes faster than further troubleshooting. Yealink phones: Menu > Settings > Advanced Settings (password: admin) > Reset Config > Reset to Factory. Grandstream phones: locate the Reset button on the underside or back of the phone and hold it for 7 seconds with the phone powered on. After reset, re-enter credentials from scratch.
Do I need a phone system (PBX) to use one IP phone?
No. A single IP phone can connect directly to a SIP trunk from a VOIP provider without any PBX or phone system software. You get a phone number, inbound and outbound calls, and voicemail. A PBX adds features like multiple extensions, auto-attendant (IVR) menus, ring groups, and call recording -- useful for businesses with two or more staff handling calls together, but not required for a single phone setup. See our best VOIP phone system for small business guide for the full comparison.
Why can't I use the phone port on my NBN modem with a new IP phone?
The phone port on your NBN modem (typically green) is an analogue FXS output connected to your ISP's own VOIP service. It is designed exclusively for traditional analogue handsets. An IP desk phone is a completely different type of device -- it connects to your network via Ethernet and uses the SIP protocol to communicate with a VOIP provider. These two systems are not compatible. Plugging an IP phone into the NBN modem's phone port will not work, regardless of the phone model.
What is the difference between an IP phone and a cordless phone?
A cordless phone (such as a Panasonic or Uniden from JB Hi-Fi or Officeworks) is an analogue handset. It connects to an ATA adapter or the green port on your NBN modem and uses an analogue audio signal. An IP phone (such as a Yealink or Grandstream) connects to your router via Ethernet and communicates digitally using the SIP protocol with a VOIP provider. They are fundamentally different technologies. You cannot use a standard cordless phone as an IP phone without an ATA adapter.
My VOIP provider says they don't support my phone model. Can I still use it?
In most cases, yes. 'We don't support your phone model' from an AU VOIP provider typically means they do not offer auto-provisioning templates for that model -- not that the phone is incompatible. Any SIP-compliant phone can work with any SIP-compliant VOIP provider. You will just need to enter your SIP credentials manually via the phone's web interface rather than using auto-provisioning. If your provider insists the phone 'won't work', ask them to confirm whether the issue is auto-provisioning support or genuine SIP incompatibility. The latter is extremely rare with mainstream brands like Yealink and Grandstream.
How many simultaneous calls can I make on a standard NBN connection?
Each simultaneous call uses approximately 100kbps of bandwidth (G.711 codec, the standard Australian VOIP codec). On an NBN 25 plan, you have theoretical bandwidth for around four to five simultaneous calls before quality degrades. On NBN 50 or above, bandwidth is rarely the limiting factor. Latency stability (low jitter) matters more than raw speed for call quality. If you need more than three or four simultaneous calls, use QoS settings on your router to prioritise VOIP traffic over other internet use.
Can I use an IP phone on Wi-Fi instead of Ethernet?
Yes, most mid-range and high-end IP phones support Wi-Fi (802.11n or 802.11ac). However, wired Ethernet always gives more stable call quality, lower latency, and more reliable registration than Wi-Fi. For reception desks, main business lines, or any phone where call reliability matters, use Ethernet. Wi-Fi is a reasonable option for meeting room or hot-desk phones where running a cable is not practical.
Not sure which phone system is right for your business?
Get a Free Recommendation