Use your cellphone as a Proxy???? (Android or iPhone app to constantly change ip)

I have this idea and I'm wondering if something like this already exists.
My ideas is this:

An application for "smart" phones (android, iphone) that connects to the nearest available wireless network and then allows your computer to proxy through the phone. This would allow you to have cell phones traveling around town constantly switching ip addresses as they connect from one wireless network to the next.

Feedback?

sounds like it would work... Ill try it out.... thanks