Unlocked phone question with Cricket Wireless

Just a quick question.
I recently dumped my AT&T traditional wireless plan and switched to AIO Wireless (which has now become Cricket Wireless). The price is much lower per month, and my understanding is that they use AT&T's network. I bought a Nokia Lumia 520 as part of my signup process with AIO Wireless.

I'd like to get an unlocked Blackberry device off eBay. I see that there are models that are unlocked (and can be used on AT&T or Tmobile's GSM networks).

My question is this...can I take the Cricket SIM in my existing Nokia and transplant it to the unlocked Blackberry?
Or do I need to bring the new device to Cricket and have them activate it?
I"m not 100% clear on how this works.
Thanks in advance!

Giving this a bump, as I think I may have deleted one of them as duplicate lol, never the less, anyone can answer feel free.

If you buy a BB10 phone (that's unlocked,) you should have no problems. But...if you buy an older BB (like a 9900,) I don't know if Cricket plans support BIS. Older BBs need special data plans called BIS (BlackBerry Internet Service,) and typically, prepaid carriers don't offer that. In that case, I would suggest you contact Cricket.