T-Mobile is in limbo now as Sprint has decide to cast its lot with Apple. However, T-Mobile can distinguish itself as the carrier that non-iPhoners can go to if they want to avoid all things Apple.
Furthermore, it can continue to try to steal customers with low-cost plans. I've always thought as T-Mobile as an innovative force in the wireless market - willing to experiment with different ways to satisfy customer needs.
I've left T-Mobile because of the fowl taste that AT&T brings. I hope some element of T-Mobile survives should the takeover be completed as expected. If not, I might be back.
And these days, T-Mobile has a few high end Android devices that can match those available at its competitors. It just has to stay on course.