Please refer to the following Check list. 1) Check out if the phone is unlocked. You can consult unlock issue with your phone maker or original telecommunication company. 2) If your phone has 2 SIM slots, insert the SIM only into slot 1(slot 2 : empty). 3) Please Check the Profile or VPN(Setting - General). If you see any Profile or VPN, please delete it and then reboot your phone. 4) If it still does not work, please try to 'Reset Network Setting' for the USIM and reboot. 5) If it still does not work, please make an APN setting (refer to the manual) and reboot. If you can't use it even if you try it according to the manual, please contact us