Our company has two 7937 conference phones that have both had this problem at two different locations on our network. Our normal switch port configuration is :
switchport access vlan 2
switchport trunk encapsulation dot1q
switchport trunk native vlan 2
switchport mode trunk
switchport voice vlan 5
auto qos voip cisco-phone
In the above scenario the phone would bounce back and forth between a data and a voice vlan IP address, and the phone would say it couldn't contact the call manager. To fix this i had to remove the data vlan's from the switchport and then the phone acts normally.
The problem with this is that if someone wanted to plug a laptop into this location they cannot get to the data vlan.
Has anyone seen this or have any ideas?