said by ArizonaSteve:You are correct, they don't have any service outside of major urban areas. I recently drove across Texas on I-10 and there was no coverage at all past El Paso until I reached San Antonio! AT&T and Verizon cover most smaller towns and along the freeways. Sprint even has service in a few areas but T-Mobile doesn't have any service at all in most rural areas.
BTW, you are paying way too much at $75/mo. If you stay with T-Mo you should buy one of their cheap phones at Walmart with the $30/mo unlimited data plan and put the SIM in you phone.
I have a business account with Sprint so I have coverage wherever Verizon has coverage with them but with T-mo I use it for my business and use about 3000 voice minutes every month so I couldn't use the $30 WalMart plan if I wanted to. Because of this I also don't think I could rely on prepaid from any company as I can't afford any downtime or bad customer service. Thanks for the advice though.