IPhone (and iPad as well) is one of the latest and most innovative device of Apple Inc. They run special operating systems like any other Apple devices and they use special tools designed only for them. Apple devices also support Internet connection therefore they are capable for voice over IP communication, too.
Apple has special developer tools for its devices, therefore program writing is slightly different on these devices so it was not an easy task to create my own VoIP application, but Ozeki VoIP SIP SDK gave me all the background for it on this platform.
I wanted to create a VoIP client for iPhone. I became fully familiar with all the essential terms concerning iPhone VoIP clients after reading an excellent description.