Probably US Only
If how they sold the Zune is anything to go by.
But the real question is WHY?
The Mobile Phone market is ultra competitive and (apart from the iPhone) AFAIK, margins are pretty slim on each unit sold.
Henc my question Why?
Why do they want to get into this market which has probably reached maturity in most developed countries where the returns on each unit is very small and highly competitive?
They could continue to develop the OS platform but I see that being left behind unless they have (As sugested by a previous poster) completely redesigned the whole UI bit to make it work like the iPhone. Bear in mind that they have to watch out for the inevitable patents held by the likes of Apple and Nokia for the UI stuff.
This (if true) strikes me as being nothing more than a 'Me Too' stunt by Balmer.
Anyway, I wouldn't want one any way so this is a moot point indeed and no I don't own an iPhone.
Mines the Brown Coat to match the Brown Zune in its Pocket...