works perfectly as a stand-alone phone, even with BT

With eSIM calls are possible without bluetooth connection to the phone. Bluetooth headphone can be connected. So as an example listening to Spotify with watch only is possible, making calls as well.

Yes, the lte version is independent of the phone and has bluetooth

Swisscomm are the only ones who offer sSim for the watch. However, you must already have a mobile plan and then it costs an additional CHF 5 per month. Salt and Sunrise are not yet ready, their information on when they will offer it is vague. What is possible, if WLAN, telephony with WhatsApp, including video telephony.