The free version can't call back a message before it's read, or track when messages have been read.

CNN: Make your e-mail disappear

Once a track is selected, Flipboard users can read other sections while the audio plays in the background, an amazing new capability that lets people listen while they continue flipping through their Flipboard.

ENGADGET: Flipboard brings the noise in NPR-ified app update, Britta will be pleased