I would agree.
http://docwiki.cisco.com/wiki/Unified_CCE_Software_Compatibility_Matrix_for_10.0(x)#IP_Phone_Support
"The following general limitations pertain to IP phones used with Unified CCE Enterprise deployments:
- Only Cisco IP Phones are supported as contact center agent phones. As an alternative, you may choose to deploy the Mobile Agent solution to enable Cisco Unified CCE to use any phone as an agent phone. Please consult with your Cisco Sales Engineer for additional detail on this configuration."