Well… it stopped working on my Pinephone about five months ago. I’ve had the L5 for a couple of months now, but no joy here.
The project gitlab page says T-Mobile hasn’t worked since September. I tried to go to the carrier settings page, but the wiki was 404. I suspect the project is going moribund.
There is a small bright side… vmmd does send me SMS messages from 127. The messages contain coded text that undoubtedly makes sense to Visual Voice Mail. It doesn’t make make sense to me, but when I get one I know to call the voicemail number!