The Yosion Apple Peel 520 is a new wireless device that adds mobile voice and text messaging capabilities to the iPod Touch. The gadget acts as a protective skin that slips over the iPod Touch and includes a battery, dock connector and SIM card holder. Once the proper software is installed, the Apple Peel 520 adds the ability to make voice calls and send and receive text messages on your iPod Touch.
The only thing that can be a problem for some people: it requires a jailbroken iPod touch.
It looks great on an ipod touch 4th generation, check out this video: http://www.youtube.com/watch?v=yzEKMj4p3xs
More info at http://www.peel520.net/