New blocking method to stop voicemail messages
The current blocking method allows unwanted callers to leave a voicemail. This is really irritating with persistent unwanted callers who clog up your voicemail and annoy you with new voicemail notifications.
A new option which allows blocking by accepting the call and immediately hanging up should block the call and prevent voicemails from being left. A way to hide the incoming call UI should be investigated as well.
Edit:
It seems accepting the call is unnecessary. Just that the call is hung up.
Maybe other methods could be used to block voicemails from being left?
Update with solution:
I have found a way to get the desired behavior of stopping blocked calls or manually stopped calls from going to voicemail.
Go to the default Android dialer -> Settings -> Supplementary services -> Call forwarding. Press "Forward when busy" and set it to a number that is unreachable, such as "+10000000000".
This solution should work as long as your service provider allows call forwarding.