How does the LTE calling work?

Th eSIM doesn't technically have the same number, it has its own number, but the phone forwards calls to the watch.

https://support.apple.com/en-gb/HT205547

 

Yes phone calls come to the watch independently of the phone when signed up for LTE service. In fact, if you have your phone, it should ring both on your watch and iphone. Most companies are using some kind of number syncing software, so you need to have a "phone number"

If you decide to not sign up for LTE, then it will work like the ipad on wifi.

AT&T has a little bit of explanation on their site: https://www.att.com/esupport/article.html#!/wireless/KM1223159?gsi=LPjJmB0

 

No it would not work. The eSIM stands for electronic SIM, as in on the circuit board and not a separate SIM card. The watch only works with the same carrier as the paired iPhone and must also on the same post-paid billing account.

Dave