Honestly I don't know for sure, and there isn't any documentation from what I can see. However I've been thinking about this based on the following observation: If you take your Watch outside it takes a good 15 seconds or so to go from being connected to your iPhone to being on cellular (with the red X in the meantime). But if you go somewhere where it will connect to Wi-Fi instead, and then do something that requires cellular (e.g. making a call), the switch-on of the cellular connection seems much, much quicker than 15 seconds. It's as if the Watch goes into a sort of low power state where it will maintain just enough of a connection to receive incoming connections, and then in theory when you do something that requires full power cellular (e.g. make a call) it will jack up the connection. The issue that @mzanker is seeing seems to me to be related to the handoff issue that has still not been fixed and that the WSJ reviewer experienced - that the Watch clings onto Wi-Fi and won't activate cellular when needed, e.g. when making calls, but will activate cellular correctly when receiving a call. --- Post Merged, Sep 30, 2017 --- When you receive the calls, are they crystal clear or do they break up and drop? Sounds like the handoff bug to me as I mentioned in my last post a moment ago.