I've come to the conclusion that there are three complimentary form factors you'd need, 1/ phone/PDA, 2/ easily portable laptop, and 3/ full-size laptop (desktop replacement) or desktop. I do like the Athena, and could probably make it do the job of 1 and 2, as I am not a massive user of mobile phone.
You could do this with docking stations, make the phone be a mass data store, and attach to laptop or desktop. Alternatively, the only way at the moment would be to use a gigantic flash memory card or microdrive (10 to 100GB for me), carry it with a small number of readers/adaptors, and then you can have all you data and home directory on the phone, pda/zaurus, on laptop, on desktop etc.