With Cisco CallManager 3.3(2) running in the Media Convergence Server (MCS), every time a user logs into the Extension Mobility service, the Cisco IP phones reset.
This can happen if the device profile being loaded is inconsistent with the device type. For example, if you are trying to log into a Cisco IP phone 7940 with a Cisco IP phone 7960 profile, the Cisco IP phone resets twice (this is expected behavior). However, if you attempt to log into a Cisco IP phone 7940 using a Cisco 7940 profile and the problem is still observed, then the problem might be with the Cisco IP phone load.
To resolve this problem, upgrade your Cisco IP phone load to P00303020300.bin or to the latest Cisco IP phone load from Cisco Downloads.
Use this procedure to download a new Cisco IP phone load into the Cisco IP phone:
Copy P00303020300.bin to the C:\Program Files\Cisco\TFTPPath directory on the TFTP server.
Open the Cisco CallManager Administration page and enter the username and password.
Select System > Device Defaults.
Change the default load of the device in question to P00303020300.
Reset the devices in question to get the new load.
For more details about troubleshooting Extension Mobility, refer to these documents: