Currently I am with AT&T but not under contract. If I walk into Apple and buy the unlocked Verizon iPhone 5s with a contract, how long does it take before I can start using that phone via Verizon? Am I up and running before I leave there? This may be a stupid question for all I know. I have been with AT&T since I got my first cell phone in the 1990's. I have never had a smart phone.