Does anyone have any ideas/precautions on how to go about stealing and selling pre paid phone cards?
can you just walk out of the store with them? and is there anyway to track them?

You bet; the FBI now has a dedicated division that specialises in tracking stolen phonecards. Because spending a few thousand dollars tracking it down is well worth getting back the $20 card.

What? No, just grab a stack and pocket them.
But be aware the have no value until a code is input at the register, so you're only going to be able to sell them a town over.