You will probably want to order through Verizon phone support, and make sure you tell the rep you're buying it month to month, full retail, outright. NOTHING CHANGES on your plan. Get their name. Record the call if it's legal to do so where you live. That way, if they SAY nothing changes and then it DOES, you have evidence
Some people run the numbers and find Edge a worthwhile switch: I don't. I'll cling to unlimited as long as I possibly can... which means full retail from here on out.