I just found that on the OCS PBX and gateway compatibility list that  Cisco now has 2 routers listed the compatability list specifically lists supported IOS. Now I have not tested this yet but will be interested to see how well it works.

This should be a great feature for Cisco and Microsoft. See the link below it has a link to the cisco documentation but it is a little misleading because it does not take you right there. You may have to select "Cisco Voice Gateways" Then look for Microsoft Office Communication Server 2007 version RTM to Cisco IOS Voice Gateway using SIP with T1 ISDN  They also have a guide for E1 as well.

http://technet.microsoft.com/en-us/office/bb735838.aspx