cell phone question
 

My blackberry met an untimely end a few days ago (apparently they dont like water). Anyways, I'm looking to buy a new one and was checking them out on e-bay. I see that some of the ones listed claim they're only useable for one provider (att, t-mobile, verizon, etc). How does this work, would i not be able to use a "t-mobile" blackberry with verizon service whatsoever, or does somthing like the SIM card need to be swapped out?

GSM phones can be locked to a particular carrier or even a particular SIM.