To expand the zing! user base, we've developed zing! free!  Who doesn’t like free stuff? We submitted the app during the last week of December, which coincided with Apple’s company shutdown. So, zing! free wouldn't be reviewed  until the 4th. It so happens that they got to our app very quickly and rejected it that same day (the bright side is that the process is getting faster).

For zing! free, we adjusted the layout to accommodate ads and an upgrade button. The buttons are smaller, and arranged into 2 rows of 3 instead of 3 rows of 2. In addition to adjusting the layout, we only used 1 combat sound per theme (instead of 3 in the paid version).

To entice upgrades, we provided previews of 'bow chicka bow wow' and the shock.  Those buttons are “greyed” out and only playable once per session. Once users press the button, a popup appears and lets them know that this sound can be used more if they upgraded.

This is the email we received:
Zing! FREE cannot be posted because it is a beta or feature-limited version.  Free or "Lite" versions are acceptable, however the application must be a fully functional app and cannot reference features that are not implemented or up-sell to the full version.

Luckily we got rejected because realized that there was a typo on our pop up screen (see the second screenshot). Since receiving that email, we altered our app and resubmitted it on 1/12/10. We now allow users to use the sounds without any restrictions. And as a result, our app is now in the app store as of 1/15/10! Apple's approval process is finally getting faster.