iOS 12.1.2 Update Available to Download for iPhone
Apple has released iOS 12.1.2 to resolve several issues with some newer iPhone models. Specifically, iOS 12.1.2 resolves issues with eSIM activation on iPhone XR, iPhone XS, and iPhone XS Max, and also resolves some cellular connectivity issues with those same model iPhones in certain geographic regions. It’s possible that iOS 12.1.2 also includes other bug fixes or changes that are not specifically mentioned in the release notes.
Update for 12/20/2018: Apple released an updated build of iOS 12.1.2 for iPhone, the new build is 16C104.