Until June 29, Best Buy is offering to trade iPhone 4/4s for a free iPhone 5.
See the article for other terms and conditions.
The free phone deal is a result of two ongoing promotions happening at Best Buy right now. In May, the store began offering any iPhone with a two-year contract for $50 off, bringing the iPhone 5's usual $199.99 price down to $149.99. Now when a customer brings in an iPhone 4 or 4S they will get a $150 trade-in credit, making the iPhone 5 free.
But there are some caveats. Customers have to be eligible for an upgrade at Verizon, AT&T and Sprint (no T-Mobile) to get the offer and they will have to pay the carrier activation fees and sales tax. The credit can't be used towards a different phone and the deal is only offered at physical Best Buy or Best Buy Mobile locations.
See the article for other terms and conditions.