I have this issue with the cisco 7911 ip phones, not been able to register with CCME.
Cisco 7960G can register with out any issues.
The Problem seems to appear when i add configuration on the switch for the interfaces.
when i assign the switch Ports with one Vlan 7911 registers.
when i put both acces/Voice vlans on the interface the phone just cuts itself from the network.
here is a config of one swith port.
description === Production Network ===
switchport access vlan 10
switchport voice vlan 1
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
mls qos trust device cisco-phone
mls qos trust cos
spanning-tree bpduguard enable