iphone 5s question

I have a 2-1/2 year old Samsung that I'm going to replace with a new iphone 5s I bought at Walmart. I was at a Walmart closest to us in Dixon, Illinois and I spoke to them about activating the new iphone. They informed me that this phone will use AT&T as a provider for the iphone and there is no service in our general area For AT&T. If this is the case this phone is useless to me. How do I identify whose towers are used?