My CP 7960 has a very interesting problem, one which I simply just don't understand. When the phone boots up everything works fine, connects to my SIP callmanager and runs well for at least a little while. After sometimes minutes, or sometime hours the phone will just stop accepting calls from other phones. Other phones wont even get the ringing sound and it will just go to voicemail after about 20 seconds. If another phone user leaves a message for the one with issues the message waiting light wont go on, nor will it recieve calls until it is reset.
Interestingly enough the phone can still make calls when this is happening, just not take them.