I recently bought an iPhone 5S under the family plan on T-mobile for my son. He has been with Sprint for a while now and I recently got him an iPhone 5S with Sprint back in April. It just came to me that if i pay the ETF that I can keep the phone and have it unlocked, so I can activate it with T-mobile. My question is, do i have to pay the ETF to have it unlocked or do I have to pay ETF + whatever I own of the phone? It would suck if i have to pay both, but i just want to keep the phone from sprint, have it unlocked, and insert a T-mobile sim, thanks in advanced!