If you're buying a new phone and your old phone still works fine, a good way to defray the cost is to sell the old phone to any one of the many secondhand phone retailers. If you're trading in an old iPhone for a new one, for example, Apple will offer you some credit for the old phone directly. According to a report from 9to5Mac, the company will soon begin offering money for Android phones as well, incentivizing some of the platform switchers that Apple talks about during its product events and earnings calls.
The report doesn't have much other information about the extension of Apple's trade-in program, noting only that retail store employees are currently being trained and that it will begin "in the coming weeks." Employees will help new iPhone buyers transfer their contacts from their old phones to their new ones, but "other data will have to be moved by customers." Apple has several guides to facilitate the move available on its site.
The drawback of Apple's existing program is that what the company gives you is rarely competitive with market rates on eBay and other phone reseller sites. Apple would give $35 for a working and relatively pristine unlocked 32GB iPhone 4S, but a look at completed eBay listings shows those phones going for between three and four times that amount (minus whatever fees the service charges). The official Apple program won't accept anything older than an iPhone 4, either, so there may be other restrictions based on the specific model you're attempting to trade in.
