Samsung's new smartwatch thing looks too big and bulky. I haven't worn a watch in years, so I'm not going to jump back by wearing a giant thing that barely lasts a day.
So first, be small and unobtrusive.
Our home phone (wow, we still have one of those!) is thru Xfinity/Comcast. One great feature is if someone leaves a voice mail, it uses voice recognition to trans-scribes it and sends and email with the message as text. Very nice.
First, the iPhone should simply do that for any voicemail. Then a notification on a watch (in addition to the notification on the phone itself) can show the text of the voicemail without listening.