Switching to the Mac[c] The Missing Manual
For making Internet-based phone calls, it's hard to beat Skype. If you call from one computer to another, you pay absolutely nothingno matter how far away your recipient is.
Luckily, you can download a Mac version from www.skype.com. From there, you can audio-chat with all your Mac- and PC-using Skype buddies until you lose your voice.
Tip: iChat, Apple's own instant-messaging program, also offers free audio chats. If you and your buddy both have Web cams or videocameras, in fact, you can make free, Internet video calls. See Section 11.3.7 for the details.