both variants (Bluetooth and 4G) can connect to network via Bluetooth on mobile phone
while 4G variant can connect to network without the phone around, but a phone pairing is required for initial setup only
According to the site
Wi-Fi/LTE connection is required on Galaxy Watch3 and feature requires pairing with smartphone. Galaxy Watch3 4G connects exclusively on EE*, Vodafone** and O2***.
*Standalone voice calling on 4G model requires an EE PAYM voice plan with data subscription to access the ‘One Number’ service. For initial set-up, wireless network and pairing with Samsung Galaxy smartphone 2017 and newer required.
**Available to all Vodafone Pay Monthly Mobile customers on a Red Plan. You will use the allowance from your current PAYM or SIMO plan to call from your Samsung Watch. For initial set-up, wireless network and pairing with an Android smartphone with OS Android 5.0 or newer and at least 1.5GB RAM required.
*** Standalone voice calling on 4G model requires an O2 PAYM plan with data subscription. Your Samsung smartphone must also logged into your Samsung account, be switched on and connected to the O2 network. You will use the allowance from your current PAYM or SIMO plan to call from your Samsung Watch. For initial set-up, wireless network and pairing with Samsung Galaxy smartphone 2019 and newer required.
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