My router is an innbox v50u with 2 ports for telephones, the phones are able to make calls but I am unable to receive them. I've tested the sip settings with an android app and the 2talk softphone and it works fine which leads me to believe it may be an issue with the router OR the handset.
The handset is a Uniden Elite 9035+1 withn rj11-rj11 cord running from the base to the router's telephone port.
Here is the settings page:
