The only problem with that idea is that for some reason a lot of people want these devices to be able to make and receive traditional phone calls. They'll rather have a phone they can surf with than have a more appropriate Internet tablet...
No! Because I don't always have access to the Net, and I don't see that happening for the forseeable future either. Actually, having the phone as your PIM-base is not too bad an idea: I have my phone with me always -- OK, almost always -- and my tablet most of the time, so close interaction of those two seems logical to me. And having the data on my phone means that I don't have to hope and pray for an internet connection whenever I want to check my schedule.