Anyone have any success with trading in old electronics?

There are tons of advertisements for sites like gazelle.com that will trade cash for your old electronics (cameras, phones, etc). Anyone have any success or real difficulty trying this? I have 2 old iPhones gathering dust, and would rather get a few bucks than toss them in the trash. Are these places generally reputable? Do you get your cash, and if so, is it generally a decent trade?

Whatever you do, make sure all data is erased.