To my knowledge, communication between phone and the watch is still via bluetooth if both devices are within coverage distance. The beauty is, for lte version, calls could be made directly from the watch without the need to pair it with the phone. It's standalone. As for e-sim, basically there's no physical sim where phone's id ( maybe IMEI ) is tagged with provider's esim number. It's secure and use less space in the phone. In future, I believe all phones will use esim technology.
