Someone asked me this morning why Apple had not come out with a cellphone (we'll ignore the awful Motorola phone that had some iTunes support). The cellphone marketplace is extremely crowded and highly competitive; Apple would not have any real advantage in marketing an Apple-branded cellphone, and phones need more than the gorgeously simple iPod interface.
But my other guess is that Apple has plans to skip over the phone completely. Take a look at this mysterious patent over at Engadget. The patent is listed by Apple, but it refers to the iPod constantly and seems to be some kind of videoconferencing add-on to an iPod. The illustration shows an external camera, but that's not likely. Here's my guess (and this is just speculation).
Apple already has miniaturized its iSight camera; they are built into the lids of all Apple laptops now. The same camera could easily be added to an iPod with any difficulty at all. Apple has been a pioneer in WiFi, and could easily add wireless Internet connectivity to an iPod. Finally, Apple has superb videoconference software with iChat, a mature product that comes with every Mac.
So the next generation iPod comes with a built in camera, WiFi connectivity, and iChat software. Walk into any WiFi hotspot, pick someone off your buddy list, and call them via iChat. When they answer, you have a full duplex, two way videoconference with a high quality Internet protocol. In fact, you can talk to anyone with a similarly equipped iPod, but also anyone connected to the Internet who uses the same platform independent chat protocols that iChat uses.
With the iPod more popular than beer with college students, an iPod with video chat capabilities would fly off the shelves and deepen the iPod's lock on the youth market for portable gadgets.
With an iPod, why bother with a phone?