Cisco 7921 IP Phone frequently getting disconnected from Wireless

[Sunish Nair]

Hi,

Facing one issue at one my site, while users are roaming with their Cisco 7921 IP Phone they are frequently getting disconnected and phone is giving this message "Leaving Service Area". Recently CUCM has been upgraded to Version 9 from CUCM 6. Current WLC Model is 4402 and Version is 4.X. Below i am mentioning all the details....response really appreciated.

Wireless Information:

Cisco 4400 Series WLAN Controller
AIR-WLC4402-50-K9
Software Version: 4.2.130.0

AP/LAP: Cisco AIR-LAP1252AG-E-K9

IPT Information 
Firmware Version for IP Phone:cp7921g-1.4.5.3.loads
cucm version: 9.1.2.11900-12

[Brian Meade]

The phone firmware change is probably the biggest contributor.

Take a look at the deployment guide which has a lot of good best practices for the wireless settings:

http://www.cisco.com/c/dam/en/us/td/docs/voice_ip_comm/cuipph/7925g/7_0/english/deployment/guide/7925dply.pdf