Patent No. 8,687,299 has been granted to Apple today for "Bayonet attachment mechanisms," i.e. a bayonet mount that is able to securely attach lenses to an iOS device, such as an iPhone, iPod touch or iPad.
A bayonet mount is a fastening mechanism which is typically seen on cameras, used to attach lenses to the camera body.
At the moment, there is no adjustable camera lens system in existence for smartphones, although there are lots of third party macro lens products that consumers can buy to clip onto their smartphone.