I've been using
Skype for talking between myself (in Bermuda) and family friends at home in the UK and in the States - and find it works really well computer to computer. I also like the P2P idea working behind the scenes. When I later saw stuff like Vonage, I was surprised people were charging for it - what is the cost/Quality like?
The only time I've seen lagging on Skype is when a conference call is in progress - otherwise, it's always been remarkably good.