Can I legally sell my cell phone?

I just renewed my provider contract and got a new model Blackberry. The thing is, my provider sold out to AT&T and they will be giving me a new compatible equivalent phone in 2 months.

This current phone will work with Verizon and other providers (just not AT&T’s network) and it is not “provider labeled”. It seems a waste to shove it in a drawer and I’m aware that I can donate it, though the current service said they don’t want it back, but I wonder if it’s legal to sell it to someone who uses a different network?

I know these things can be tricky sometimes. I paid for it. Do I own it?