If reinserting the SIM card, rebooting the smartphone or updating the iPhone, and other general troubleshooting cannot fix the problem, call the service provider and be sure that your SIM works. If the problem still persists you should take the SIM to Apple support for the hardware check. Some problems may be long-standing signs of a damaged device, including a problematic SIM card reader, which will need repair or exchange to fix Iphone Sim Failure issue.