With Verizon there is a different phone number assigned but it still bills to your iphone account. It's pretty transparent but what is important to know is these key differences:I haven't activated Cellular on my Watch yet. How does it work? Do I get a different phone number for the watch? Or can the same phone number be shared between the phone and the watch?
The cellular watch will have a higher base cost.
You don't have to activate the watch on your account and it will work to make calls through your iphone radio. This means that to use the watch as a cell phone you must be within Blue Tooth range.
Your cellular watch will always use the BT through your iphone even with the account for the watch activated except when your iphone is out of range.
Cellular activated, allows you to make and receive calls to your watch if you leave your iphone at home.
Even with your watch on it's own number any calls made to your iphone number will automatically go to your watch if the iphone is out of BT range. You don't need to supply your watch number to anyone. I don't even recall what my watch number is.
If your life style is that you frequently go out without your iphone, then activating the watch is a good idea to receive calls, texts, and have LTE internet on the watch. If not activated and you are out of BT range, your A watch will not be able to communicate except to local BT device like airpods. .