Phone Shows "No Service" or Won't Register

Step 1: Check the Physical Connection

Most registration failures start with something simple. Before touching any settings:

1. Confirm the Ethernet cable is plugged into the LAN port on the back of the phone — not the PC port. The PC port is a passthrough for a computer and does not carry the phone's own traffic.
2. Press the cable connector firmly until it clicks. A loose cable is a common cause of intermittent failures.
3. Try a different Ethernet cable. Cables can fail without any visible damage.
4. Try a different port on the switch to rule out a dead or misconfigured port.

Step 2: Verify PoE Power

Yealink phones can be powered by the switch via PoE (Power over Ethernet). If your switch doesn't support PoE, or if the PoE budget on that port is exhausted, the phone may power on partially but behave erratically.

1. If the phone is powered by PoE, try plugging in the included power adapter instead. If the problem resolves, the issue is with PoE on your switch.
2. Check your switch's PoE status page to confirm the port is delivering power.

Step 3: Confirm the Phone Has an IP Address

If the phone isn't on the network, it cannot reach the 3CX server at all. Check what IP address the phone received:

1. On the phone, press OK or Menu.
2. Navigate to Status › Network.
3. Check the IP Address field.

If the phone is showing 0.0.0.0 or a 169.254.x.x address, the problem is at the network layer. Check the switch port, VLAN assignment, and DHCP server. From a computer on the same network, try pinging the phone's IP — if the ping fails, the issue is network-side, not phone-side.

Step 4: Check the SIP Registration Status

If the phone has a valid IP but still shows "No Service," the problem is likely with SIP registration. Check the error code the phone is reporting:

1. On the phone, press Menu › Status › SIP Account (exact path varies slightly by model).
2. Note the registration status and any error code shown.

Step 5: Check for SIP ALG on Your Router

SIP ALG (Application Layer Gateway) is a feature on many routers that attempts to modify SIP packets in transit. In most cases it causes registration failures, dropped calls, and one-way audio — even though it was designed to help. It must be disabled.

1. Log in to your router's admin interface (typically at 192.168.1.1 or 192.168.0.1).
2. Look for SIP ALG under Advanced, Firewall, or NAT settings — the exact location varies by router brand.
3. If SIP ALG is enabled, disable it and save. Reboot the router, then reboot the phone and check registration again.

SIP ALG is the single most common cause of intermittent registration failures and one-way audio on business VoIP systems. If you recently changed routers and calls stopped working, check this first.

Step 6: Verify Firewall Ports Are Open

The following ports must be open for outbound traffic from your network to the DVGVoIP 3CX server:

If your firewall or router is blocking any of these, calls will fail or audio will be one-way. Check with your IT team or contact DVGVoIP if you need a list of specific IP addresses to whitelist.

Step 7: Factory Reset (Last Resort)

If all else fails and you suspect the phone's configuration is corrupted, a factory reset will clear everything and allow the phone to re-provision automatically from the 3CX server — provided the MAC address is registered.

1. On the phone, press Menu › Settings › Advanced. Enter the admin password (admin by default).
2. Select Reset to Factory and confirm.
3. The phone reboots, wipes its configuration, and starts the auto-provisioning process from scratch.
4. Wait 2–5 minutes for the phone to provision and register.

A factory reset will not work if the phone's MAC address is not registered in the 3CX Admin Console. Contact DVGVoIP before performing a reset on a newly purchased phone.

Still Not Working?

If none of the above steps resolved the issue, contact DVGVoIP with the following information so we can investigate quickly:

• The phone's MAC address (printed on the label on the underside of the phone)
• The error code shown under Menu › Status › SIP Account
• The phone's current IP address
• Whether the issue is affecting one phone or all phones on the same network

Need Help?

Open a support ticket by emailing support@dvgvoip.com before calling — this helps us resolve your issue faster. Or call (807) 700-7111.