If you experience problems (e.g. no dial tone) using your Voip phone after installing a new router (where you will get a new IP address from your Internet service provider), the following may help resolve the issue.

Disconnecting and reconnecting the phone adapter (ATA) may not solve the problem. In this case, you need to log in to the ATA (find the IP address of the ATA from the router’s local network status page). The password may very likely be ‘admin’. Go through the details of the configuration to see if anything is suspicious. Finally reboot the ATA from the configuration tab. You may notice your ATA will now be assigned a different IP address by the router. Hopefully your Voip phone should work again after performing the above steps.