OK - the rest of this is if this link doesn't help: https://www.blackberry.com/SoftwareD...ient=Z2fedFddN
That's a list of most of the BlackBerry providers globally, although the links on the page are to their firmware download page.
It would have been more helpful if you had given a hint as to what continent you're on let alone what country, but you managed to squeak out enough info that I might be able to get you started.
First, TURN ON THE DEVICE! The main screen should have some indication as to what service provider the device was originally with.
Since you said it's a GSM SIM device, it's most likely either T-Mobile or Cingular (although there are other providers too). If it's one of those, you're in luck. Simply contact them - they may have arrangements with a provider in your country as they both have fairly extensive global coverage. That said, it will probably be very expensive!
If it's neither of these providers and you can tell who the provider is (like Rogers), contact them. If this is the case and that provider has no solution, you'll probably need to get the device unlocked and go with either T-Mobile or Cingular.