It works, the speaker is really quiet though. Even when I was at home with no ambient noise I had to hold the watch up to my head to hear it better. The other party said they could tell I was talking through my watch but that I sounded alright. I’m hoping Garmin can boost the call volume a bit with a software update, without pushing the driver beyond its limits of course.
Maybe I'm wrong but when music is playing on the watch, it's seem to be a bit more louder, so I'm sure they can pre amplify the voice during a phone call.
