Apple Watch no sms when away from phone

The Apple Watch CANNOT send SMS TEXT messages by itself. The cellular chip in the Apple Watch just does data, but SMS is part of the traditional voice cellular technology, and the Apple Watch does not use that technology, rather it uses Voice over IP (VoIP).

Because of this, the Apple Watch uses iMessage to relay SMS send/receive requests between the Apple Watch and the iPhone under the covers.

So you MUST have BOTH the iPhone and the Apple Watch signed into iMessage using the same Apple ID, or there is no way for the Apple Watch to ask the iPhone to send SMS messages, and there is no way for the iPhone to tell the Apple Watch that an SMS messages has been received.

You do not personally need to use iMessage, but as a transport relay, the iPhone and Apple Watch need it for SMS messages.

The text starting with 2. in my previous reply comes directly from Apple at the bottom of the web page pointed to by the URL in my previous message. I am not making that up, I am just doing a copy & paste.

Use your Apple Watch without your iPhone nearby - Apple Support

2. To receive SMS, MMS, or push notifications from third-party apps on your cellular Apple Watch, your paired iPhone must be powered on and connected to Wi-Fi or cellular, but it doesn't need to be nearby. You also need to be signed in to iMessage on your iPhone to use Messages on your watch.