This work is licenced under a Creative Commons Licence.
I have just tested out Fonebank to recycle (or sell) my old mobile phones. It's a simple service where you send them your old phones, and they send you money in return. I was impressed.
The Fonebank site is easy to navigate and use, and everything is simple - they give quotes for broken/working phones as you specify, and are clear on what is required for a phone to be working (you do NOT need to send things like a charger, and they don't care if the battery is poor). Obviously if you have an old phone, or even one that was cheap initially, you might get very little for it (£4 for a working Samsung E700 for example), but they gave me £33 for a working SonyEricsson K800, which was very good compared to the going rates on Ebay.
I placed my order on Monday morning, and posted them off by special delivery that afternoon (you can post Freepost, but at your own risk etc.), they emailed me telling me that they have received the phones on Tuesday, and a cheque arrived on Wednesday. Quite brilliant. There are a few similar services around (though Mazuma appeared to be the only one with a website that was as intuitive), so it's worth shopping around to see who will give you the best prices.