Yes, but you need a subscription, usually around 5 chf, to be activated with your operator, if it is not already included; then the watch works completely independently of the phone, the only flaw is that the battery drains faster than the Bluetooth connection
Yes, according to Samsung, it is set up for this: "The LTE versions of the Galaxy Watch4 and Watch4 Classic can be used for making phone calls or surfing without a connection to a smartphone".
It is important to have an appropriate mobile subscription with your provider.