[MrEdd]

There is no reason whatsoever for the phone part to be detached.

There will also be smaller phones, but people are carrying around six and seven inch phones right now. 14nm dies will shrink a full windows machine to that form factor.

[adorno]

There is no reason whatsoever for the phone part to be detached.

Perhaps not, but, it would be a lot more convenient to be using the "detached" phone component, while also using the phone's provider of service (the small form factor PC) for many other things at the same time. When a device is brought up to one's ears, the form factor becomes, mostly, just a phone. A PC that can serve as a PC and a tablet and that can be used as a "super-computer", should not be constrained to a simple phone, just because it carries the phone component internally.