I dunno. I think they're capable of picking up vibrations, but I like to think my first betta hears me. When he sees his reflection, he goes nuts until I say "shh, shh" and he backs up and doesn't mess with his reflection anymore. I know they don't have ears, but the more I think of it, I think they can pick up vibrations (which is why I don't let my little cousin tap-tap-tap on the aquariums)
Well, they kind of have "ears." Fish have otoliths (we have them in our inner ears) that help them determine which way is right side up and help them sense movement. Their lateral lines, however, are the major vibration detectors. These are found on the sides of their bodies. I'm sure they also can sense vibrations in their swim bladder, not unlike feeling heavy bass music booming in your chest.