VoipBuster

VoipBuster offers a simple tool for OS X to make cheap phone calls.
VoipBuster is a free program that uses the latest technology to bring free and high-quality voice communications to people all over the world.

When you use the free VoipBuster software, you can call regular phones in various popular destinations for free or call at an incredible low rate to any other phone on the planet.

You can also call all your online friends (pc-to-pc calls) as long as you like, for free.