While everyone is busy discussing the Tablet Wars, which will undoubtedly break out soon enough, I think we are approaching faster than ever to what everyone already know is the next step in computing.
It's not far from what Microsoft named "Three Screens and a Cloud": the central hub, the Cloud, is the place where the data actually is. The user is able to access the data using either a PC, a TV or a Phone, either at home, work or in the metro.
What the tablet wars (or the phone wars, for that matter) are trying to determine is "how" is the user going to access the data. The concept, however, is already being sold as something certain, regardless of Stallman's opinions.
If we take it for granted, then what are the phones - or the PCs, or the TVs - good for? If we start reasoning in term of anything as a service, it doesn't really matter if your phone or your pc has 1Gb or 512 Mbs or RAM, as long as it is able to stream you multimedia representations somebody computed somewhere. Try OnLive to get an exact idea of what I'm speaking about.
This said, it seems to me this OS-Hardware war should transform itself in a form-factor war, which is most likely going to end up with some degree of flexibility for the mobile end (someone will prefer smaller factors, like phone, while someone will still like the larger screens laptops can offer and so on), and pervasive docking stations everywhere. Once you plug your phone on the dock you get access to a larger screen and to all your data and software in the cloud. Maybe your local-office cloud, maybe your personal cloud or maybe even some sort of "service provided customized cloud", it doesn't really matter.
However, phones will still play a critical role as KEYS. If we want to think about secure cloud computing we have to think about pervasive, high security encryption. Phones and other devices, then, will just become our personal wallets, storing access data we can unlock with a password which in order will unlock all our cloud stored data. That is, until we start to actually use biometrics... but that's another post.