nokia lumia windows phone OS and microsim question

wondering if anybody has any experience with this phone overseas / traveling around the world? i tried searching on this forum and nothing specifically about them.

my dad has the lumia 710 and loves it after trying out a bunch of other phones recently. says it just does what he wants well and the wireless connect is flawless vs an ipod touch he has. the more expensive model 900 got rave reviews recently. fwiw, i'm not interested in android / google or apple for a variety of reasons - don't want the thread hijacked by zealots in either of those camps ;)

i'm interested in the 710 b/c i can pick one up for about $180 used here (the states), get it unlocked and it will do what i want. don't need anything fancier really. it's quad band gsm so i know it's compatible with all the global networks from a hardware perspective.

since i'm not a big cell phone user, my main questions are:

1) this phone takes microsim format sim cards. my current 5 yr old cell phone uses std size sims. when traveling rtw (every where literally which is why i'm not specifying any particular regions) this upcoming year, will it be difficult finding carriers that provide microsim cards?

my guess is that nw providers have customers with a wide range of devices that need different format cards so they probably carry both formats but i really don't know.

generally speaking, does anybody know if there is a trend to go microsim in the future and drop the bigger size sim cards going forward?

2) the OS on the lumia is windows phone 7.5. as i said, my dad loves the thing. ez and intuitive to use. sharp display. etc. since the lumia is quad band, i know it will work with the variety of gsm hardware networks around the world, but i was wondering if something about the OS itself might need to be modified by a given carrier to make it work with their specific network? any truth to this? my friend has an ATT phone here in the states. It's android but he says they modify the OS to make it work with their services and he presumed that if he unlocked it and tried to drop in a different sim for a different carrier, it might not work?

does anybody have knowledge of windows phone OS working on foreign networks around the world to help assure me this won't be an issue?

3) how ez is it to change the language on the phone

4) would it be better to wait and pick one of these up on the road (maybe cheaper outside the states)?

sorry for all the questions. windows phone / nokia lumia weren't getting much love on this forum.
thx