Hi JP,

The ISC interface is well defined. The interoperability that you are talking about does depend on the release spec that the CSCF is based upon. Here are the 3GPP/3GPP2 links for ISC:

http://www.3gpp.org/ftp/Specs/html-info/23228.htm
http://www.3gpp2.org/public_html/specs/X.S0013-002-A_v1.0_051103.pdf

Depending on the kind of SIP Application, perhaps the most important thing for a developer to adhere to would be the SIP Private Headers (P-Headers RFC3325, RFC3455). For example, you will find that older SIP applications (and SIP stacks) don't work at all with the latest OpenIMSCore.

I haven't come across any tutorial type documents explaining the Gm, Sh and Mx interfaces - For this I would suggest a hardcover book from Amazon.com -> http://www.amazon.com/s/ref=nb_ss_gw/002-4096502-0664024?url=search-alias%3Daps&field-keywords=ims

Hope this helps.

Regards,

Mike