Does my watch need to have its own phone number to call 911 with a hard fall?

Absolutely not!

The Apple Watch need not even be a cellular model.

To call emergency services, your Apple Watch or nearby iPhone needs a cellular connection, or needs to have Wi-Fi calling turned on and Wi-Fi coverage available. With an iPhone 14 or iPhone 14 Pro, even Emergency SOS via satellite may be used.

If you have a GPS-only watch, you will need two have the paired iPhone nearby. Otherwise a GPS+Cellular watch will call on its on(if setup properly).

Identify your Apple Watch - Apple Support

I have a GPS only Apple Watch. I have had it call 911 when I had a "False Positive" event. It just used the iPhone in my pocket to make the call, but the call was made using my Apple Watch, and the conversation happened on my Apple Watch.

From my response above:

”To call emergency services, your Apple Watch or nearby iPhone needs a cellular connection, or needs to have Wi-Fi calling turned on and Wi-Fi coverage available. With an iPhone 14 or iPhone 14 Pro, even Emergency SOS via satellite may be used.”

Hello, yes I read that. Thank you.

There are two parts to cellular service - the data and the ability to make calls. My question is whether the phone that the watch is paired with needs cellular data or just needs to be able to make a phone call.

Thank You.

A cellular connection, I.e. data, or does the phone just need to be able to make a phone call?

Thank you.