Skype

I'm a big fan of Apple's iChat. I have an iSight and it does a very excellent job of video conferencing to the UK, no problems whatsoever.

However..I'm getting more impressed with the whole Skype space.

Skype is a p2p voice (soon to be video) system and allows free skype-to-skype calls. It also has the capabilities (for a small charge-around 2c per min, called SkypeOut), to call regular phone numbers. They also have a means for people to call you (again for a small fixed charge) called SkypeIn. You can choose a regular phone number and calls get routed to the Skype application. You also get free voicemail when you purchase SypeIn. (called Skype Voicemail)

As you travel, even though you have say a NYC number, calls get routed to your hotel in say San Francisco. Very cool!

This is a LOT cheaper than services like Vonage, which AFAIK seem to follow regular phone companies and charge around $25 per month.