That didn't work - but I'll post what did that fixed it.
I downloaded Audio Manager (Free) just to see what all the volume levels were at - turns out the "system" volume was at zero and everything else was fine. The problem is there's no "system" volume setting that I'm aware of under the normal settings menus. When I turned it up with audio manager the keypad and dialpad sounds returned.
I think it has something to do with the slide to unlock/slide to silence lock screen stuff as I did accidentally slide the silence toggle the other day but figured when I slid it again it was fine. Silly me.