If incoming calls are not ringing on your SIP phone, the phone may not be registered in the Tel-One network.
Check the following physical aspects of the phone:
Power cycle the phone (unplug power cable and Ethernet).
Can you reach the internet (a web site not visited in the last week) through your computer that's next to the phone?
Checking network settings on the phone, does an IP address (e.g., 192.168.1.xxx) appear in the display? (for Yealink, click OK button).
Make sure Ethernet cable is plugged into the “internet” port, not the “PC” port on back of the phone.If it still fails, move the phone’s Ethernet connection at the router to a different port (may be a problem with the router port).
If the phone is still not ringing:
Checking the SIP phone's display panel, make sure
a) Do Not Disturb is turned off, and
b) Call Forwarding (in Feature menu) is disabled.