Speech to text

Nope. The only way you can send any kind of media other than plain text over SMS/MMS is to do so over the latter protocol. The receiver can always use their text-to-speech engine to read the message out loud, but it won't be a recorded message (i.e. your voice).

If you mean sending a text with your voice, then yes, you should be able to use voice dictation on your watch to dictate a text.
 
Yes this is what I wanted to do, my hands was freezing and I couldn't tap a message so I pressed the microphone to dictate a message but it sent as a mms voice message x

Sent from my SM-N986B using AC Forums mobile app
 
press the microphone icon on your keyboard rather than on the text messaging app. also did you mean for this to be in the galaxy watch 4 forum?