Apple has just released iOS 10.0.3, a minor update to iOS 10 intended to fix cellular connectivity problems with the iPhone 7 and 7 Plus. Unlike most iOS updates, this one is available exclusively for the newest iPhones, since older iPhones and iPads running iOS 10.0.2 don't seem to be affected.
The problem seems to affect US users on Verizon the most consistently, and most users' complaints say that the phones drop their LTE connections and either fall back to 3G speeds or lose connectivity altogether. Reports of similar connectivity problems have also come from AT&T users, and late last week, Bloomberg also reported on complaints from Chinese users who were losing their signals. Apple's release notes don't mention any particular countries or carriers, but iOS 10.0.3 will hopefully resolve the problems for everyone.
Apple is also working on a major update to iOS 10, version 10.1, which adds the "portrait mode" feature to the iPhone 7 Plus' dual-camera system and makes other tweaks. That update is currently in its third developer beta and will be released later this fall.