I know, I’m really bummed out about this too!
We’ve had this functionality before but it has resulted into some major bugs and errors during registration process, so we decided to nip it in the bud.
We might bring those buttons back though!
But for the time being, please use the good old login + password combinations.
The Open Mic will remember you the first time you log in.
In case you forget your password your can always request Password Reset.
Hopefully we’ll manage bring back Twitter and Facebook signup soon.