It would be rather cumbersome. Velcro 2 iPods together, put it in your pocket, and see how practical it would be to lug around.
Once the iPhone is released I fully expect it will be disassembled quickly and shown on the internet. Depending on the number and type of Flash chips, it
might be possible to double the internal storage. If so, expect to see a couple of places pop up that offer to mod your iPhone.