Sprint has a pretty solid network in most markets, but they also have a metric crapton of debt.
What it comes down to, is there isnt enough spectrum to have three fully competitive carriers. The merger of T-Mo and Sprint will give them a huge leverage point on spectrum. T-Mo bring 600, AWS bands, as well as 1900 PCS blocks, Sprint brings 2.6, 900 and 1900 PCS blocks.