Ajmal Mundu, 15, of Fremont, shows off his new iPhone 5. 

Patrick Tehan/MCT

Best Buy is running a promotion where customers can save $50 instantly with the purchase of any iPhone with a two year activation on Verizon, AT&T and Sprint. That means the iPhone 5 would be discounted to $149.99.

Here's the best part. Customers who trade in any working iPhone 4 or 4S today will receive a guaranteed $150 in trade-in credit. Combine that with the $50 instant savings and your phone is practically free. The only out of pocket cost would be any applicable sales tax and carrier activation fees.

To take advantage of the deal, customers must be eligible for an upgrade and activate the iPhone 5 on a two year contract with Verizon, AT&T or Sprint. The trade-in deal is only good today. 

Go to www.bestbuy.com to find the store nearest you.