How do iPhone can video chat a mac computer?

Apple made "FaceTime" for video calling from MAC to iPad 2, iPhone 4, iPod touch or MAC. All you need is an Apple ID and an e-mail address and that's it!

Another way for video chat is "Yahoo Messenger 2.0". With yahoo messenger 2.0 you can make voice+video calls to other messenger users on iPhone 3GS, iPhone 4, MAC or other windows running systems.