Does anyone knows how many different hardware versions are out there of the N900 ?

I am talking HARDWARE, not operating system or firmware versions which, of course, there are several.

Are there documented differences (or fixes or improvements) of each version ?

Which one is the latest ? Are those versions zone/region related ?

Don't know if this is valid...but here it goes: Which one is the recommended/desired to (hopefully) get when buying a new N900 ?

This question, of course, goes hand in hand with my new N900 checkup list question.

Thanks.