1. Yes.
How do I unlock my BlackBerry? - BlackBerryFAQ
2. In that case, his carrier MUST have the BlackBerry Data Plan on that account, and you must register your BB to their network, in order to get push email to your BB.
You might be better off getting a TMo International Data Plan, and using your own SIM and Data.
1. yes, that is how it works. BIS - BlackBerry Internet Service.
2. same as always. Do you get your email on it now?
3. Yep. Just there are variables you must decide on. It will cost more (international anything costs). But it is a workable goal, people do it everyday, all over the world.