Starting a cell phone retail business
Congratulations on your new business venture. Technically you could run this business as a sole proprietor, in which case I would recommend you to pick a trade name and register it as a DBA. On the other hand, you might want to consider organizing your business under a limited liability entity, such as an LLC or a Corporation, in which case a DBA would not be necessary.
Regardless of how you organize your business you would need to obtain an EIN and a reseller permit (sales tax ID). If you start as a sole proprietor and then later decide to reorganize as an LLC or a Corporation you would almost certain need a new EIN and a sales tax ID.
Finally, NAICS stands for North American Industry Classification System, and its the standard used by Federal statistical agencies in classifying business establishments for the purpose of collecting, analyzing, and publishing statistical data related to the U.S. business economy. Your particular business would fall under several NAICS codes, I believe 443112 (Radio, Television, and Other Electronics Stores) and 453220 (Gift, Novelty, and Souvenir Stores).