I bought a second-hand Japanese version of Apple's 6s mobile phone, put it on the SMS card, and there was no signal. When I put it back on the original Unicom card, I can surf the Internet through SMS

I bought a second-hand Japanese version of Apple's 6s mobile phone, put it on the SMS card, and there was no signal. When I put it back on the original Unicom card, I can surf the Internet through SMS, but I can't answer the phone. Energy source and solution: 1. Signal or electric operators's problem. Wait for some signals. Now the call failed, so you need to redial. In this case, the previous signal causes switching and redialing. 2. Turn it off. 1. Signal problem. Try to turn it off before operating. Now press the iPhone power button to turn off the phone. Slide down. 3. Insert the electronic card and dial. Turning off the phone can solve the problem. Try to get the card with the pin or something similar that comes with the iPhone. Second, use the card pick-up pin on the right side of the iPhone, that is, punch in the card to get a clean card, and then try again according to the original position to see whether to dial. Fourth, the original China network settings. First, try to solve the problem, and try the original iPhone China network settings list. Please click on the general column. Click to enter the original column at the bottom of the regular list. Click to enter the original list. Click to select the original China net setting bar. Click the original China network settings button below to confirm. Wait for the original power supply of the system and see if you can dial the phone. 5. Hardware failure. 1. Try to replace the Zhang Tong card. Try replacing the electric card. Explain the problem of the electric card. Ask the power operator to reissue the card. 2. Replace the electric card to solve the problem. It is recommended to go to the authorized sales office of iPhone for inspection.