You're on the right track as far as looking at it from the prospective of being an investment that might not pay off for a rather extended period of time. Neither AT&T nor VZW are as dense as you think though. In Lewiston, AT&T has 4 site locations, VZW has 5, and both T-Mobile and Sprint have 2. The real advantage that AT&T and VZW (and later this year, T-Mobile) have is that they're running 700 LTE on all of those sites. The extended reach and better building penetration really show their colors when you live or work in an area that isn't in (relatively speaking here) close proximity to a serving site. Take Model city as an excellent example, whilst colocating on the already existing tower would be the best solution to improve the spotty coverage, having 800 LTE (and a nice little 1X channel for voice) on the Center Street site would change the service from spotty to reliable. I believe this (SMR deployment in the North) will transpire before Sprint starts adding some serious density to their grid.