Apple Watch cellular

A) You can switch your iPhone to a carrier that supports the Apple Watch

Apple Watch - Carriers - Apple

B) You can stay with your current carrier and use your Apple Watch without cellular and have all the features AS LONG AS your iPhone is nearby.

C) You can treat your Apple Watch as if it belongs to a dependent child (operating in a degraded mode), and get a more expensive 2nd phone number from another carrier that supports the Apple Watch Family Plan.

Apple Watch Family Plan

Set up Apple Watch for a family member - Apple Support

Set up a family member’s Apple Watch - Apple Support

Some limitations: Cannot receive SMS/MMS messages, as that depends on a fully paired iPhone. Messaging is pretty much limited to Apple’s Messages, unless the messaging service provides an Apple Watch app. Alarms, alerts, notifications on the iPhone are not sent to the Apple Watch. Apple Pay via a credit card is not available. Also not available: Medications, respiratory rate, irregular heart rhythm notifications, ECG, AFib History, Cycle Tracking, Sleep, Wrist Temperature, Blood Oxygen, Walking Steadiness, Audiobooks, Camera Remote, News, Shortcuts, and the double tap gesture.

I am personally using option B, as I always have my iPhone nearby and I have never felt I needed to leave my iPhone at home.