This question is really about the availability of CDMA signals vs GSM signals and what company(s) have contracts with the owners of those signals.
So the best way to figure out what your coverage will be like is to contact your preferred carrier and ask if they have contracts for signal in the areas you will be traveling most often. This isn't information your average ring-in-the-nose 22 year old cellphone salesperson will know. You need to find a company rep with some technical knowledge. It is a little difficult to do but well worth the time.
I have had ATT, Verizon, Union Wireless. There maybe CDMA signal available between Gillette and
that I wouldn't pickup where Verizon doesn't have a contract. That said, my experience going north to
from Gillette, the GSM (ATT, Cellularone, Union Wireless) signal is good for about 10-15 miles north of Gillette on Hwy 59. The CDMA (Verizon) signal is good for about 20 miles. From that point north to Broadus, neither a CDMA or a GSM signal is present.
At the Broadus chicken-coop/rest area, there is both a GSM and CDMA (Cable & Communications Corp.) signal. A Verizon phone in this location can pickup the CDMA signal. Straight Talk which uses CDMA likely doesn't have a contract with Cable & Communications Corp., which is why that phone doesn't work there. GSM signal on an ATT phone works pretty well.
Once you cross the hill north of the Broadus airport there is no GSM signal until you get very close to the SY school. The signal is good for about 3 miles either side of the school. There is no GSM signal from that point until you get to 10 mile hill just south of Ochsners. From there on into
the GSM signal is excellent on my iPhone 4.
The CDMA signal north of Broadus is better but still intermittent; for example, you can pickup the CDMA signal on the hill above Volborg but lose it once you get down on Pumpkin creek. You will pick it back up about 4 miles south of the SY school and it is good until the Beaverslide/Powderville turnoff. The CDMA signal starts showing up intermittently about 5 miles south of the Tongue River road and is solid from 10 mile hill on in to Miles City.
IMO, the "best value" is the phone that works where you spend most of your time. That will likely be a different company for different areas. True cellular coverage is really all about whether your carrier has a contract with the signal owner in a specific location.
The following link displays a searchable map that tells you who owns each tower when you click on the pin marker. You can then contact that company and see if they have a contract with the Carrier of your choice.http://www.cellreception.com
[This message has been edited by Richard Bonine, Jr. (11/21/2011)]