AT&T offers service in 21 states. The average download speed on AT&T is 10 Mbps. AT&T offers service in 107,329,041 Households. Your best chance of finding AT&T service is in Illinois, their largest coverage area. You can also find AT&T in Kansas, California, Oklahoma, and many others. It is a DSL provider, which means they deliver service through your traditional phone lines. Internet service enters the house through a common phone outlet, which is connected to a DSL modem. From here you can connect your wifi router or use an Ethernet cable.