You can use the Sound Recorder App to record sounds generated from the Audio Function Generator. However, for playback, you can only have the Sound Recorder App open. Otherwise, you will see this message:
To resolve this problem, tap Home, then tap Audio Function Generator, then tap the "X" in the upper-right corner to properly close the Audio Function Generator App. Then, return to the Sound Recorder App by tapping Home, Accessories, and Sound Recorder. You should now be able to play back your recording.