From David Strom.

Vonage adds another feature to this list, which is having a phone number that you can transport with you around the world. All you need is a broadband IP connection and your Cisco router (your home phone number is tied to its MAC address). You go for a business trip someplace, and you can be making and receiving calls from your phone as if you were home. This comes in handy if you travel overseas and don't want to pay the usurious rates that hotels charge for international calls.