VoIP implementation in iPhone

• How to implement VoIP in iPhone using code? 开发者_开发知识库
• Is there any code to implement it?

Use pjsip :). It's a SIP library written in C. You must compile the source for iphone, it is described in the docs here. After that take a look at a very basic sample application here. It isn't very hard to use even if you don't know C or how to compile libraries.

UPDATE Beware that PJSIP uses GPL as it's license.

Check Siphon which is described as Home of the World's first free SIP/VoIP application for iPhone and iPod Touch 1 and 2.