You do need a Sim card. In most cases ,if a new Sim card is needed for the phone -usually you can just get one from your service provider usually at no cost to you and they set you up via your account . I had a problem with my Sim card and my carrier AT&T gave me a new one at no cost and set me up. Your Sim card is the memory of your phone that holds your phone number -without it,it cannot detect who you are. Walmart can also provide you with one as well . Good luck