When is MS going to make a new flagship for T-Mobile?

I'm on T-Mobile at the moment cause they have the best bang for buck and currently using the S4. I had a 920 on AT&T but I sold it when I cancelled the service and at the time T-Mobile had no good Nokia WP. So the question is when is MS/Nokia/Anyone coming out with a legit Flagship phone because all it seems like T-Mobile is getting from MS are weak budget phones that nobody wants meanwhile all the other companies' flagships have a presence there.