Game Center / Alert Notification

Is there a callback that will give my scripts notification of when a system dialog opens and closes?

Basically I want to turn off my music while the user is logging into Game Center or viewing the Leaderboards.

I'm looking for a callback for when the seen loses and regains the focus.

I've tried onDialogPush / onDialogPop, but since they dont work I'm assuming they are for GUIs.

Cheers,
Sam