I put a few of these together back in 2017. The classic BT vanguard model was the perfect size for housing a Arduino based midi controller. The handset of course also doubling up as a seriously lofi microphone.
I still have the orange one, I believe I have the grey one knocking around some where and the beige one that was passed on to a friend I think found it’s way into the hands of different musicians in the North West over the past few years.