At AT&T Wireless, trade in your previous-generation iPhone (in good working condition) and you'll get up to a $300 AT&T Wireless credit. The newly-released iPhone 6 starts at $199, and the iPhone 6 Plus starts at $299, with a new 2-year contract. Redeem the credit and you can grab either of the latest iPhones for free. That beats a similar mention from Verizon from two days ago (which only had enough credit for the cheapest model) and is the best deal we've seen on the iPhone 6 so far.