Scenario: You have a 4-line family plan with AT&T. Two lines are off-contract and qualify for a discounted phone upgrade. T-Mobile has a promotion whereby they will pay ETFs of up to $350 per line for any customer switching from AT&T/Verizon/Sprint. If I would like to switch to T-Mobile, is there any reason not to purchase two iPhone 6 devices on AT&T (likely $99-199 each) before I make the switch? I understand AT&T would charge an ETF of $325 per line, but T-Mobile is willing to pay ETFs of up to $350 per line for customers to switch. Is there anything stopping me from taking these two iPhone 6 devices from AT&T to T-Mobile? Is there any reason not do this? What am I missing here, if anything?