Apple

Enable WiFi calling and message forwarding on the phone.

As long as you have your phone nearby, yes, you can

Go into iPhone watch app, scroll to phone & touch. Toggle on settings on for “mirror my iPhone”. On iPhone settings -> cellular toggle on WiFi calling & also calls on other devices. On your watch settings make sure you are on same WiFi network as iPhone.

I can create or respond to txt’s & email w/ my non-cellular watch and also make & receive calls, both at home and away from home. Generally, I prefer using the phone rather than watch for this.

I don’t know that all these settings are necessary since they don’t involve Bluetooth. I’d experiment with them. But when my watch happens to be on a different wifi then none of that stuff works. That could be due to phone being too far away from watch at that moment.

If the watch is connected to your phone via Bluetooth, you can “make calls” in the same way you could make calls with any other Bluetooth accessory such as headphones or a car stereo

Text messages should just work as well, same basic idea