The largest and most common phone companies in the United States are T-Mobile, AT&T and Sprint, and if you choose one of their services, you will find coverage in post places in the United States.  Ultra Mobile has the best pricing; however, their signal is not as strong in areas outside of large cities.

AT&T:
https://www.att.com/

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T Mobile:
https://www.t-mobile.com/

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Sprint:
https://www.sprint.com/

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Ultra Mobile:
https://www.ultramobile.com/