This is the A1428 model of the iPhone 5, introduced by Tim Cook at an Apple Special Event on 12 September 2012. This variant is sold only in the United States, Canada, Puerto Rico and Mexico because of the LTE bands it supports; the N42AP is sold in other countries, as well as the United States and Canada.
There are actually two versions of this model; when T-Mobile USA began to carry the iPhone 5, Apple made a tweak to this model to support HSPA+ on AWS bands. A carrier update enabled LTE over AWS for all of these iPhones, but using HSPA+ over AWS requires a new unit. Apple provides instructions [Archived 2013-04-14 at the Wayback Machine] to check if an iPhone 5 can use HSPA+ on AWS. The name used in firmware is iPhone5,1.