i have at&t wireless. i just lost my phone, and my dad wont let me buy a new one, and he wants me to get a free one b/c he thinks i'll lose it again. but everywhere i see, there are free phones, but you must buy a contract to get it for free. can i buy a used at&t compatible phone on craigslist or something and then get at&t to activate it? what is an unlocked phone?