Unless you’ve been living under a rock (or don’t go online much), you’ve probably heard of Skype, but have you heard of the Gizmo Project? If not, check it out. It is very similar to Skype in concept, but it has one big difference: it is standards based.
It is built by the SIPphone.com folks, so when you register you’ll get a SIP telephone number as well as your username. That means that people using other SIP phones, even on other networks in many cases since they peer with each other, can also call you, and vice-versa.
Although the software itself is still in beta, it seems pretty stable on the Mac at least. Since the network underneath it is very stable, the call quality is great. I have made computer-to-computer calls and a transatlantic call from San Francisco to the UK.
So, download it and try it out (you get $0.25 of free credits so you can test call-out calls too). If you do try it, call me (Gizmo name: john94501). I don’t have it on at work yet (the Linux client is still in development), but leave me a message and I’ll call you back 🙂