Curious about how different prepaid carriers coverage compares? Here are the official coverage maps for all the nationwide prepaid mobile operators in the US. Click a map to go the original on the operators site.
While comparing nation coverage is interesting and maybe even useful what really matters is if there is coverage where you live, work, party and vacation. With the exception of Simple Mobile all the carriers have detailed block level coverage maps on their sites. For Simple Mobile you can use the 2G tab on T-Mobile's detailed prepaid coverage map as long as you ignore the striped beige "Sevice Partner" areas.
StraightTalk (also Net10) (GSM-T = T-Mobile, GSM-A = AT&T, CDMA-S = Sprint, CDMA-V = Verizon)
Verizon (also Page Plus, RedPocket CDMA, Selectel) Light lavender roaming which is included on Selectel, extra-cost on others
AT&T (also H2O, Red Pocket GSMA, Airvoice, Jolt, Pure TalkUSA, Cricket (Brown = 3G phone required)
T-Mobile (also Ting GSM, MetroPCS) includes lots of no extra cost voice & text only roaming, see GoSmart map for data coverage.
GoSmart Mobile (also Ultra Mobile, Spot, Simple Mobile, PTel, Lycamobile, T-Mobile and MetroPCS data)
Boost Mobile (also Virgin Mobile, EcoMobile, Sprint Prepaid, FreedomPop, Simple, Kajeet, Total Call, RingPlus)
Updated 12/24/2015: Removed old Cricket CDMA map as the network has been shut down.