would i be able to unlock the blackberry 7520 , because i want to switch providers over to tmobile , would anyone know if this is possible ?

Nope. The 7520 runs on Nextel's iDen network and is not compatible with the GSM network that T-Mobile uses. It can not be done.

You could, see www.bongowireless.com but the 7520 is an iDEN BB works on iDEN networks only. Completely different from TMo's GSM network your going to have to purchase a new BB if your going to make the move.

alight , thanks , anyone know if the 8700 would work on tmobile , considering the only provider that has it now is cingular ?

Yes - check out the 8700 forum. If you can get it unlocked, it will work fine on T-Mobile.