I was thinking it would be cool to have a physical credit card swipe using a Square dongle that dumps the card info to say mtgox and buys that amount of bitcoin and also manages send/receive and maybe multiple backup of your bitcoin. Even cooler if it can interface with a few major banks or (shiver) paypal so you could also downconvert to dollars, euro, etc.
The geekiest phone really should have the geekiest payment app, the existing app gives a good example. https://mtgox.com/mobile