After posting the T-Mobile coverage maps, we received word from the field that Sprint also has a map of their towers. It appears that folks in wide stretches of North Dakota have one tower to share between them, but their rugged, North-Country nature lets them suffer in silence.
No word yet on if Verizon is offering a snail trail of where that "Can You Hear Me Now?" guy has been.
Sprint Tower Maps [Sprint Thanks, Brent!]