Tethered cell phone is all I used last year when I was unable to get WiFi. Verizon, LG6100 phone, using charging cable form eBay and DataPilot software (worth it for the dialer, I've had problems switching back and forth from high-speed to normal speed using DUN...the modem initialization strings are different).
High-speed is pretty reliable everyehere I've been east of the KS/MO line, and in SD. Iowa/Nebraska were pretty much major highways only. Basically, anywhere the phone shows Verizon Wireless...which is a lot of the eastern half of the country.
Normal-speed is reliable through most of the plains -- with the exceptiuon of NW OK and the part of Texas where no one seems to work.
FYI: AllTel and Verizon roam to one another. In fact,t he dialer string the TV staiton is using for their cell phones is the Verizon QNC string, and they are AllTel phones.
None of this takes into account EVDO, though. Honestly, I'm not too concerned about that. The data speeds have been sufficient most of the time to keep GR3 caught up, and if I need more, I stop and use Wi-Fi. It's SO all over the place in towns of any size...and in a lot of towns of NO size! <VBG>