Who Refurbishes AT&T Refurbished iPhones?

So, I'm interested in getting an iPhone on the cheap, but I need more details about refurb details. (I've called AT&T, but I'll rather get another source of info than from an AT&T sales rep)

So, who refurbishes the used iPhones AT&T sells? http://www.wireless.att.com/cell-phone-service/packages/packages-details.jsp?qpackage=sku3270244&qsku=sku3270239

AT&T says all the refurb units have a minimum of 90 days warranty, who covers that? And if Apple covers that warranty, will I be able to extend it even if it is a refurb from AT&T?

Thanks,

Dave