If you're able to make a voice call and send SMS with the same SIM, that's an indicator that you should be able to register in the area. My recommendation is to first confirm that the Telit module is attempting to register on the right network (AT&T). For this, issue "AT+COPS-?" to find all of the networks available. Then, "AT+COPS=1,2,"310410" to force the device to attempt to register on AT&T. Try that and let me know what you get.