The Apple Watch functionality has improved over time. An iPhone used to need to be left on and connected for Cellular to work on the Watch. I was under the impression that with advances in eSim and Software Updates the watch could now make and receive calls without any dependence on the iPhone, except perhaps for the occasional software update). Recently I learned that with AT&T that NumberSync is necessary and call do not ring on cellular unless the iPhone is left on and connected to the internet.
What is the current state of cellular connectivity on Apple Watch? According to Apple.com Cellular allows you to leave your phone behind and just use the Watch, but does the phone need to be online somewhere?