I'm not sure how necessary it is to flash the Verizon firmware on it. It may be best practice, for the sake of being able to follow the WAP/MMS word for word, but Amp'd does not lock their phones.
I can state this with high confidence: you can get an Amp'd Q to work on Cricket by following the steps on this forum. Plus, I'd imagine an Amp'd Q could be picked up a lot cheaper than any other carrier's right now.