Updated: Dec 9, 2019
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.
These affected units were manufactured between September 2016 and February 2018 and sold in China, Hong Kong, Japan, Macao, and the U.S. See below for iPhone 7 model numbers that are covered in this program.
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.
For more information on this service notice, please check out this Apple support post here.