Work bought me a new phone (HTC Mogul) and I've gone a bit nuts, customizing it. One of the apps I installed is Skype. Unfortunately, I don't know anyone that uses it so I haven't been able to try it out yet. I won't post my ID here but if you want to give me a call, send me a PM.
Skype rules. I use it at home for all of my work calls. Costs me about $60 per year for the unlimited calling throughout the US + my incoming Skype phone number.