At T-Mobile, buy one Apple iPhone for T-Mobile and add a line to get an Apple iPhone SE for $0 via this mail-in rebate. (Alternatively, get a $400 credit toward the purchase of any additional iPhone. You'll have to pay all applicable taxes and fees on both phones. The rebate will arrive as a pre-paid Mastercard within eight weeks.) That's a savings of $400. Click here to view all terms and conditions. Deal ends June 30.