US Cellular has great coverage back home (Maine) but shoddy coverage where I live now (New York) and T-Mobile vice versa. I've been on Google Fi for the past ten years because it is the only option (at least when I last looked) that jumps seamlessly between the two, and at a reasonable enough price (for a guy who doesn't use much data). If this merger makes another carrier that has good service throughout the northeast, that could change the game for a lot of customers.
I'm not optimistic, though; the T-Mobile - Sprint merger was supposed to improve their service but ended up [0] jacking their prices.
At least as of 10-15 years ago US Cellular owned their rural markets and leased their urban markets. In NYC they are likely reselling Verizon’s network.
Google Fi used T-Mobile, Sprint, and US Cellular behind the scenes. At least, they did at the time I signed up, which was why I signed up. Sprint merged into T-Mobile a few years ago; Fi dropped US Cellular last spring.
Since then, I've stayed on from inertia. I'll probably switch to T-Mobile's $15 / 5 GB plan soon, since it's half the price I'm paying for now-no-better service from Fi and I rarely use more than 1 GB per month.
I'm not optimistic, though; the T-Mobile - Sprint merger was supposed to improve their service but ended up [0] jacking their prices.
[0] https://news.ycombinator.com/item?id=40379028