Audio support on mobile devices is ... shitty. You're right that there is no sound on iPad but weirdly enough, iPhone+Safari seems to work, at least last time I checked.

Our focus in the next 2-3 months is on the desktop clients. We'll release a OSX desktop app next week, then a Windows app after that. Mobile is crucial in the long run but unfortunately we can't do much until the browser vendors provide better support for playing sounds.