Apple has determined that a small percentage of iPhone 7 devices may show "No Service" in the status bar (even if cellular coverage is available), due to a component that has failed on the main logic board.
If your device exhibits the symptom described above, Apple will repair your device, free of charge. Your iPhone will be examined prior to any service to verify that it is eligible for this program. This program only applies to iPhone 7.
You can check here if your device is eligible.
Choose one of the service options below to have your iPhone 7 repaired. In all cases, your iPhone will be sent to an Apple Repair Center for service.
For more details, check here.