SIP call using C# and Objective-C

I am p开发者_如何学运维lanning to do a SIP video conferencing application that works on SIP protocol , between an iPhone client and C# server ? Is that possible and is there example on C# server for handling SIP?

Yes http://sipsorcery.codeplex.com/.

Given that SIP is a network protocol, any SIP entities implemented in any language will be able to communicate. So your Objective-C and C# stacks will happily communicate with, say, a Delphi stack.