Transferring to another carrier using device from another carrier

Hi,

Am obsessiong over getting a BB, am in Switzerland and the only 2 versions of BB here in Orange (carrier here) are the Pearl or 8820.
The javelin looks great but since there's no release date for it in the US yet, i'm not even going to imagine when it would land in switzerland! So meanwhile i've set my eyes on the Curve and was wondering if anyone knew if a foreign device would work on a swiss contract? Ie i would buy it in the US and then just buy the contract here in Swiss....

Of course wehn i ask this to the sales assistant they prefer to tell me that it will cause too many problems and they reccomend buying from them...but of course they want to make a sale so i was wondering if anyone elsehas done this with positive results???

Thanks for any comments!