T-Mobile struggled so much before the iPhone was finally available for the un-carrier. These days, when it comes to aggressive promotions, the other carriers are always second or third to follow after T-Mobile. Just in time for the iPhone SE, T-Mobile is offering a 50% discount for any second iPhone to customers who purchase any iPhone on an Equipment Installment Plan (Not leased devices). T-Mobile will send you a rebate in the form of a pre-paid VISA card for half the cost of any second iPhone, even if the second iPhone is more expensive than the first one. Tech Grapple confirms this...
Source: http://www.gsmarena.com/deal_buy_one_iphone_get_the_second_one_50_off_at_tmobile-news-17635.php