Looking at all the reactions from first time users, it really made me want to try those. Quite large and apparently under 100g (to compare, the average weight for prescription glasses is 20-40g). That being said, nothing compared to a Quest. I would use this just for being able to see avatars when I talk to someone (I already take my calls walking using the Meta glasses).
But if someone calls you on the phone, they are just sending their voice to you, there's no Avatar from them, except for one your software invented. The one that you're looking at is disconnected from the actual person.
They could be video-calling you or using their own pair of glasses with their own avatar. It doesn't necessarily have to be audio-only, especially when it will get easier and easier to do this.