Seems like T-Mobile still has a for sale sign up. Not too long ago, AT&T tried to buy them and the FCC denied the merger. Then Sprint attempted to buy T-Mobile but didn't move ahead over fear of the FCC denying their buyout. Recently we've heard that Dish is interested in merging with T-Mobile which would make sense seeing as they have a boatload of spectrum and nothing to do with it, yet. It looks like Dish has some competition for T-Mobile now, which historically hasn't been good for Dish.
Reports coming out this morning from Reuters states that Comcast is in talks with T-Mobile USA and Deutsche Telekom. Who is the majority owner of T-Mobile US. The report also states that the parent company is in talks with other companies as well. It's said that because Comcast is in a better financial situation, and they'd be able to buy out all of T-Mobile US shares from Deutsche Telekom. So the company sees Comcast as a better option than Dish. That also shows us that DT is still looking to get out of the US very soon.
After Comcast pulled out of attempting to buy Time Warner Cable earlier this year, it's clear they have their eyes set on mobile. That could be a bad thing. Comcast is nothing like T-Mobile. They aren't changing up the industry really, they are more like Verizon or AT&T, and stuck in their own way of doing things. The only way this would really work is financially, as Comcast does have a boatload of money. Comcast doesn't really have any spectrum either, especially compared to what Dish has. Which is about the same as what T-Mobile has, actually.
A deal with Comcast would likely send the wrong message to the industry as well as their customers. But there's no doubt that the extra cash could help T-Mobile compete better with the duopoly of AT&T and Verizon. While the deal likely wouldn't be done before the 600MHz auction next year - if it gets approved - it could definitely help T-Mobile's financials.