Apple's mobile phone can't make calls or answer phones. Without any hint, it can receive a short message, but it can't open it. What should I do?

If your iPhone cannot make or receive incoming calls, first of all, it is recommended that you check the cell phone signal icon in the status bar at the top of the screen. If you don't have a cell phone, or it says "No Service", please try moving to another location. If you are indoors, try going outside or near the window. Please make sure that airplane mode is not turned on. Choose Settings from the home screen, and then turn off Airplane Mode. If this doesn't work, please turn on the flight mode, wait 15 seconds, and then turn off the flight mode again. Turn off iPhone, and then turn it on again. Press and hold the Sleep/Wake button on the top of the iPhone for a few seconds until the red slider appears, and then drag it. Then press and hold the Sleep/Wake button for a few seconds until the APPle logo appears on the screen. If the SIM card is locked, please click Unlock and enter the PIN code of the SIM card.