Hi Peter,
CCM 4.1(3) does support the 7921G depending on what SR's are installed or if you are at CCM 4.1(3) with no SR's. This will determine what steps are necessary to add support for the 7921G as a selectable phone model/type;
When deploying Cisco Unified Wireless IP Phone 7921G for the first time, you must install the 7921G Device Pack to add the new phone type to Cisco Unified CallManager.
To make the Cisco Unified Wireless IP Phone 7921G available in the Cisco Unified CallManager system, you might need to upgrade your system with the latest DevPack patch for your release of Cisco Unified CallManager. Check the ReadMe file (cmterm-7921-sccp.1-0-1-Readme.htm) that is posted with the firmware version 1.0(1) for more information.
http://www.cisco.com/en/US/products/hw/phones/ps379/prod_release_note09186a00807f361c.html
Here is the info for the Device Pack that you will need;
4.1(1) - 4.1(3) Upgrade to 4.1(3)sr1 and install device pack.
4.1(3)sr1 - 4.1(3)sr4b - **Install device pack 4.1(36)
4.1(3)sr4d and later has support for the 7921G
From this excellent Readme doc for Firmware 1.0.(1);
http://ftp-sj.cisco.com/cisco/crypto/3DES/voice/ip-7900ser/cmterm-7921-sccp.1-0-1-Readme.htm
Hope this helps!
Rob