How do the major cell carriers' customers rank from most D to most R?

[I spent the winter writing songs about getting better]

I'd guess:

T-Mobile
Sprint
Verizon
AT&T

T-Mobile is by far the most D because their coverage is limited outside urban areas, and since they are known as the cheapest their customers are probably more low income. Sprint is also urban-based and their unlimited data appeals to younger people. Verizon has pretty strong coverage everywhere, so demographically they are probably most similar to the country at large. AT&T is the most R since I understand their customer based is disproportionately in the South.

[Adam Griffin]

For awhile, Sprint was the only company that allowed people to sign up with no credit whatsoever (a huge deposit was required, though: larger than any of the others). Anecdotally, there was a point where I didn't know a single white person who had Sprint. I know that businesses also used Sprint/Nextel, though. Trends may have shifted in recent years, however.

T-Mobile definitely is the most Democratic of the big three, especially now that it's prepaid.

[Kevin]

it's not on the list but Cricket Wireless would def be the most Democratic imo. Given that they market themselves as a cheap alternative to the bigger carriers along with the fact that most of their stores are in lower-income urban areas.

Ex. in the Washington DC area there is like only 1-3 between NOVA and MoCo while there numerous ones in NE/SE DC and Prince Georges County MD.

[Skill and Chance]

Wouldn't Verizon be the most R?  They have a combination of high end products and the best (sometimes the only) rural service available.