This may be a concept, but I want someone to actually make it for any present or future tablet out there: An optional foldable keyboard that acts as phone handset. This is how the it works:

The keyboard is physically independent from the tablet itself, just a peripheral device that you can carry around folded in your pocket. However, it doesn't have any independent functionality. It can only work while connected wirelessly to the tablet. And that's the beauty of it: I can imagine myself carrying the iPad 3G on my backpack, ready to receive calls, and then this cellphone-keyboard in my pocket. In fact, if you add a full screen to its outer shell, it could even act as a secondary display for the tablet. Ah well, maybe in 2012. [Yanko]