No service for my iPhone 7 . Replaced SIM card and still having periodic no service

Hi on iPhone 7s there is a wide spread issue that prevents the iPhone from getting carrier service. But there is a repair program for this meaning you can get your iPhone replaced by Apple for free. https://support.apple.com/iphone-7-no-service

See if this applies to your situation: https://support.apple.com/iphone-7-no-service

Schedule an appointment at your Apple Store Genius Bar. For certain model iPhone 7, this is a known issue and if your phone qualifies, Apple will actually fix or replace it for free.