If I am not mistaken you can take the phone back once right? I don't believe you can keep exchanging the phone every 14 days. I thought it was you could exchange the one time, but you were stuck the next time.
Might be the store(s) I go to, but within 15 days, you can terminate your contract, return the phone, pay the restock fee, and go on your merry (Or, pick another one, and start over).