On my current setup, I have 7911 & 7940 Cisco Phones using an Asterisk PBX (a standar SIP PBX).
Therefore, I have not CallManager, instead, my phones are using SIP and connected to a SIP PBX server.
Problem is that, althought I have the phones setup to re-register each 60 seconds, sometimes the phones lost the register and can not receive calls (althoguht they can call for them).
If I connect to asterisk and check for the SIP status of the phones, the PBX show the phones that have error as working correctly (as being registered) but they are not, since they can not receive calls.
That is a serious problem, because althought the employeer/user can do normal calls, he is not aware that he can not receive them.
Once i reboot the phone, the problem is solved, and the phone is registed correctly for another couple of hours (even days) and then, is disconected again.
Any hint ?