Two days ago, the growing popular software "Skype"; by the company of the same name, finally released a Beta version for the Macintosh (OS 10.3.5 and later). This is after only 9 months where our friends on the Windows, Linux and Pocket PC platforms have been enjoying the features and functionalities of VoIP with Skype.
The creators of Skype are the same ones who created one of the most popular Internet software "KaZaA"; a P2P software that people used to exchange documents, MP3, movies and images.
The Skype team further enhanced what they learned from KaZaA and introduced a bunch of other technologies to produce a VoIP client that automatically locate the shortest path between Skype users.
They also have a service called SkypeOut where you can call any telephone, either fixed line or mobile, at a very low cost.
So if you have time and a microphone attached to your computer do give this software a try, while you're at it you can drop me a line (Skype ID: "vinko66").