I have recently used three phones from LHC to Parker, and to the I-10 through the US-95 farm area. Nothing was as good as my Sprint, although it did roam often. Get Sprint but pay the extra $5 per month for FREE unlimited roaming. Roaming must not exceed 50% of total usage. Of the 75 mile trip, I was without a signal for perhaps 5 miles. Most of Parker worked.
Nextel does not have service once you leave Havasu city limits until the I-10.