Yes. AT&T is America’s biggest nationwide mobile network.
Your plan can be used across the entire United States (including Hawaii), as well as Puerto Rico, US Virgin Islands, Guam & Mariana Islands.
To check coverage in a specific area just click on this link: http://www.att.com/maps/wireless-coverage.html
(The coverage map shows the scope of your coverage area. Map depicts an approximation of outdoor coverage. Actual coverage area may differ substantially from area shown on map, as coverage may be affected by terrain, weather, foliage, buildings and other construction, signal strength, customer equipment and other factors which do not allow AT&T to guarantee coverage or network availability.)