I saw some rather old questions about Nokia and SIP which were mostly left unanswered, but since I have some experience I wanted to share it for other guys using Nokia phones.
Pretty much all Symbian/Nokia phones after N95 don't have a 100% built-in SIP settings, so in general all of them support SIP but you cannot set it up without additional software which is installable from the link below:
http://www.developer.nokia.com/Resou...ications.xhtml
It should be pretty easy to follow Nokias instructions on istalling it and setting up. I have personally tested Nokia N95 (long time ago) which had a problem with automatic re-establishment of lost SIP connection. Currently I'm using Nokia E7 and Nokia N9* which both work perfectly for me with Quadro PBX. If you have any questions I might be able to help with, feel free to ask. I will do my best to answer.
* N9 is not Symbian, this one is Linux based.