To activate an AT&T GoPhone, visit the official website of AT&T. The activation can be done online irrespective of whether it is a new GoPhone account, an upgrade or an additional number added to existing GoPhone account.
Before activation check if SIM card is inserted into the phone, and the phone is switched on. Next, check if phone is activated by browsing the Internet without using Wi-Fi. Make sure all contacts and photos are backed up. Go to Att.com/activations. Next, select the activation type, and enter the wireless number and ZIP code. Click Continue, and then follow the prompts to complete the device activation.