New Mobile Phone Problem

I recently bought a Samsung GSH T309 from a friend and found out later on that it doesnt work all the the service providers in Guyana, only one, Digicell. I have always been with another provider (GTT) and i need to know if there is a way to make the phone work with both providers.
The phone works fine with the Digicell chip but when i insert the GTT chip the phone icon on the screen appears but it is striked out in red.
What can i do the fix this?

thanx in advance.

Perhaps your service provider set it such that you can only use that phone with their service? Try contacting them, they should be able to help.

ok then...

thanx