I recently bought (quite occasionally) Nokia N97 at eBay and decided to replace my beloved N95 with N97.
After a week of using I have to say, that I'm satisfied. Today I configured VoIP on N97, here are some links:
http://www.winkstreaming.com/en/n97_sip/ - thi link is quite usefull and informative
If you have any questions, just ask.