Most new mobile phone buyers are now purchasing smartphones, and while many of them are first time buyers or people upgrading from feature phones, some are invariably ditching their old smartphone. First, don't even think about throwing any type of electronics in the garbage. Landfills are not designed to handle all that silicon and awesome gadgetry. Besides that, you really have three options. Give it away, donate it or recycle it.
If none of your relatives or any of your buddies want to take a crack at your oldie, there's always Web sites like Freecycle. Freecycle is like a local hub for people to find free stuff in their neighborhoods. Just post about what you want to give away and then you can haggle with people who want your stuff or work out whatever details you need to.
If you're thinking of giving it to charity, check out Cellphones For Soldiers. It's a non-profit that works with a recycling firm to donate mobile minutes and recycled phones to U.S. service members. As for recycling, go to the EPA Web site for info on recycling centers. Before you do any of these things, you should make sure your phone's data is completely erased in a secure way. If you still have an instruction manual for your phone, it should tell you how to best delete your contacts and personal info, but if you don't have it you can check the manufacturers Web site. ReCellular, the company that works with Cellphones For Soldiers also as info on how to delete all your old data.
Be sure to double check to see that all the info was erased if you do a hard reset. One good way is to give the device to somebody else and let them fumble with it for a minute to see if they find anything. Now you can be rid of your old phone! Tell us in the comments if you've gifted an old device and have an amusing anecdote about it.