dude..u just get it unlocked and it will work fine...
its d country code which prohibits using it on other networks...
as for buying plan...lots of other countries require it,aint gona explain ..but in Pakistan u dont need to buy any plans as there arent any..
like i bought blackberry pearl 8120 from abroad long time ago...when i came back to pakistan,i put any sim but it just wont work...i got it unlocked and using it ever since