Where can someone buy a refurbished iPhone?

When I go to Apple's [webpage for refurbished and clearance products](http://store.apple.com/us/browse/home/specialdeals) , I can find links to buy Macs, iPods and iPads, but none for buying refurbished iPhones. Is it possible to buy a refurbished iPhone: * online, on the Apple Store? * in a physical Apple Store? * online or offline with a phone carrier? * other options?