Actually, VoIP phones have been around for a while, but they have been relatively obscure and/or clunky. Vonage offers an adapter box that plugs into your computer, and then lets you plug any "normal" phone into it. An easy way to continue using a plain old telephone, but you end up with yet another box, power adapter, and cables to further clutter up your workspace.
The Ipevo Free-1 phone is certified to work with Skype, one of the more popular free VoIP services, and is dead simple. The cord has a USB connector on it. You plug that into your computer or USB hub, fire up your VoIP software, and talk.
I'm looking for a slim, lightweight handset that I can use for travel. At night, I could fire up my laptop, connect to the Internet via the hotel broadband connection, and make calls from my office phone number, retrieve messages, and work the phone as if I was in the office.