I have a few question before I buy my blackberry! Think you guys can help?

I been trying to find a good deal on a blackberry for a while now and I think I finally found it. I found the blackberry 9700 (unlocked) at target. The reason it was so hard for me to find a deal is because I want to get it prepaid, so now that I found an unlocked one I am going to set it up. Also mostly want it for blackberry messenger really. So if I get it unlocked and hook it up with a prepaid plan would I be able to use bbm? Secondly, what kind of prepaid companies support blackberry? (I live in California if that makes any difference)

I tried finding this information online but there seems to different answers to my questions, so far I have not found a solid yes or no. So I tried I might ask you guys for help. Thanks :)