The iPhone 5 was discontinued by Apple on September 10, 2013 and, therefore, it is not possible to get it for free with a carrier plan. It may still be available for purchase as a used item on auction sites.
Since the introduction of iPhone 6 and iPhone 6 Plus on September 19, 2014, the iPhone 5c is offered for free with a 2-year contract from AT&T, Verizon or Sprint. It can also be purchased, unlocked and contract-free for $450 with a T-Mobile SIM, or without a SIM at all. If the phone does not come with a SIM with the carrier, it will require a GSM-compatible SIM.