if i buy a used cingular blkberry 7290

can i use it with my t-mobile service?

thanks very much people.

If its unlocked, yes.

If its not unlocked, nope.

what does unlocked mean ?

im sorry for being such a complete derlict !

and if its not unlocked how can i unlock it ?

The device is locked on Cingular's network and it will not accept any other provider's SIM card. So that is the lock crap.
No how to get it unlocked. If you are currently with Cingular for more than 3 months then ask them nicely that you are visiting to other country and will be there for couple of month so I need this BB to be unlocked.
If you are lucky they will unlock it otherwise they are the wrost butcher on the street. They do not unlock no matter what.
On the other hand T-mo will unlock your device after 3 months without any problem.
and T-Mo will not unlock Cingular's devices or vice-versa.
For now lets say that no one can unlock the device other than provider who locked it
Good luck.