Updated
Quick fix
Most “no dial tone” problems on a VoIP phone come from a loose network cable, a phone that lost power, or a phone that can’t reach your phone service over the internet. Check the cable, restart the phone, and confirm your internet is up.
A VoIP desk phone gets its dial tone from your phone service over the internet, not from a phone jack in the wall. So when the dial tone disappears, the cause is usually power, the network cable or the internet connection.
Step by step
Check the screen and the lights
Is the screen on? If it’s blank, the phone has no power. If the screen shows a message like “No service”, “Unregistered” or a red icon next to the line, the phone is on but can’t reach your phone service.
Check the network cable
Follow the cable from the port marked LAN, Internet or Network on the back of the phone to the wall or switch. Unplug it and plug it back in firmly until it clicks. If your computer plugs into the phone’s PC port, make sure the cables aren’t swapped.
Check power
Many desk phones get power through the network cable (PoE). If the phone is dark, try a different wall port, or plug in the phone’s own power adapter if it has one.
Restart the phone
Unplug the power (or the network cable, if the phone uses PoE), wait 10 seconds and plug it back in. Give it a minute or two to start up and connect.
Check the internet
Open a website on a computer at the same location. If nothing loads, the problem is the internet connection, not the phone. Restart your modem and router (see how to restart a modem and router).
Test another phone
If other phones in the office work, swap cables or ports with a working phone to find out whether the problem follows the phone, the cable or the wall port.
Contact support
If the phone still has no dial tone, note what the screen says and contact us or your phone provider. The account or the phone’s settings may need to be checked.