Didn't really find a conclusive answer to this question but one of lines (currently a Blackberry) on AT&T is month to month (contract fulfilled). If I were to purchase a second hand iPhone (ebay/craigslist) will I somehow renew a contract since Iphone data will automatically be added to my account? Can i simply swap in the SIM card and continue to go month to month? How does the data plan get added? I'd like to do this to hold out until the next iPhone comes along.