Apple has decided to enter the handset trade-in / recycling game, offering credit towards their own products. The Apple Reuse & Recycling Program non-Apple products as well as iPhone and iPads, with customers able to do the trade-in at their local Apple store or via the new web portal.
Admittedly, having had a poke around the site and investigated the amount Apple are willing to give you for certain handsets, it looks like you could get more money selling your phone on eBay for someone else to use. Of course, if you really want to get an Apple device direct from the source, or find it too much of a hassle selling it yourself or using one of the other recycling companies like Envirophone or Mazuma Mobile, I can see the appeal of doing it this way. Just don't expect a great a whole load of cash towards your new purchase.