Apple is offering free repairs to owners of the small percentage of iPhone 7 devices that may be displaying a “No Service” notice in the status bar even when cell service is available.
The affected devices, according to Apple, must be of a specific model number depending on the region customers bought their devices and were manufactured between September 2016 and February 2018. Three model numbers are eligible for the gratis fix. In the US, Hong Kong and Macao, the model number to look for on the back of your phone is A1660. In Japan, A1779 while in China, it’s A1660 and A1780. You can find the model number on the back of your iPhone 7.
Apple also stipulates that it may require the customer to get their affected iPhones repaired in the country or region of purchase. If your unit is on the list then Apple will fix it free of charge within two years of the original purchase date by sending it to an authorized repair center. Click on this link for the complete details of the repair.
Source: Apple