The way I see it:
Apple takes an iPod, tosses a phone in it, and makes the screen a touchscreen...ergo, an iPod/PDA/phone. I understand that this is probably vastly complicated then I make it sound, but I think it's definately possible, and, as done with the iPod 5G, it can be always advertised as an iPod first, PDA second (since we've had iCal/Address Book sync for a while now), and phone third (unlike the ROKR or the SLVR).