I've seen a lot of questions about this on this forum lately so I thought I would address it. First and foremost, Apple does not sell refurbished iPhones. Also, 5K does not necessarily mean the iPhone is refurbished. The only person ( In the US ) that you can purchase a refurbished iPhone from is AT&T. And humorously, Apple does not recognize AT&Ts process of refurbishing. So when you purchase a refurbished iPhone from AT&T your Apple warranty is only good for one year from the ORIGINAL PURCHASE DATE of the ORIGINAL PURCHASER of the iPhone when it was brand new. Okay, so what does a 5K serial number really mean? When iPhones are returned to Apple they completely disassemble them and do a thorough examination of each individual component. Damaged components are tossed. From there iPhones are assembled using used ( but in new condition ) and brand new components and then they are reserialized with a serial number beginning with 5K. Furthermore, there are some iPhones which come straight from the assembly line and assigned a 5K serial number. A 5K serial number simply designates the iPhone as a replacement ( service ) iPhone. So when you get an iPhone that begins with a 5K serial number it is just as good as a brand new iPhone, just simply designated as a replacement. AT&T refurbished iPhones on the other hand will have a normal serial number and may arrive with some cosmetic damage as they are simply given a visual examination for major cosmetic damage, and a quick flip through the OS. I hope this helps anyone that had any questions.