I cannot get visual voicemail to activate on GOS on the Pixel 8 Pro. The carrier is T-Mobile. It works fine when running the stock Pixel 8 Pro android OS. I'm fully aware of the carrier features page and nothing there is helpful for this. The Google Dialer (Phone) app with sandboxed GPS doesn't activate visual voicemail either.
The specific errors are:
Google Phone: Can't update visual voicemail
GOS Phone: Can't Activate Visual Voicemail
T-Mobile Visual Voicemail App: Activating.... (spins foverever)
I've tried reverting to stock OS and visual voicemail indeed works there still and after re-installing GOS, visual voicemail again won't activate.
BTW, visual voicemail works fine with T-Mobile and my Pixel 6 Pro...