The only thing I'm worried about is whether that $120 upgrade from the 6+ to 7+ will actually happen, or whether T-Mobile will screw up the trade-in and give me the $195 they "promised". Note that so far, nobody anywhere, EVER, received a written promise to receive 24 months of $27 credits. We won't know for like 2 months and I'm betting really good odds that I'm not going to get the $27/mo credit for 24 months because I have no confidence in their process.
Go here and save a copy of the promotion AP02 under the Prior Offers section. That has all the terms and conditions about the 24 monthly credits. I have that saved, so if they give me issues, I have it saved off and can reference it later.
http://explore.t-mobile.com/promotionaloffers