Hi Axel,

Sadly support for the 7906 was not added until the CME 4.0 version :( You would need to upgrade to at least 4.0.3 to be able to add 7906 IP Phones;

Q. Does Cisco Unified Communications Manager Express support the Cisco Unified IP Phone 7906G?

A. Cisco Unified Communications Manager Express will support the Cisco Unified IP Phone 7906G starting with Version 4.0.

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/phones/ps379/prod_qas0900aecd8048f829.html

The required steps for Upgrading CME are nicely listed in this doc;

Installing and Upgrading Cisco Unified CME Software

http://www.cisco.com/en/US/products/sw/voicesw/ps4625/products_configuration_guide_chapter09186a00808777e0.html

This thread has a nice note from Paolo!

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified%20Communications%20and%20Video&topic=IP%20Telephony&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1dde8b54/2#selected_message

Why don't you start by upgrading IOS to 12.4(11)XJ4, for CME 4.1. This seems to be a highly rated and stable IOS/CME combination.

12.4(11)XW2 - CME 4.2

12.4(15)T - CME 4.1

12.4(11)XJ - CME 4.1

From this doc;

http://www.cisco.com/en/US/docs/voice_ip_comm/cucme/requirements/guide/33matrix.htm

Hope this helps!

Rob