I could see cds working - if you can repeat out loud. I know I remember something better if I repeat it.
"My name is Sally"
"Hi Sally, nice to meet you"
If I don't repeat someone's name, or a phone number I won't remember it.
I've never heard a lesson on audiotape or cd, but I imagine that they don't just keep rattling off words & sentences without a space that you are supposed to repeat what you heard.
I could see you sitting on the bus with your earphones on, then suddenly blurting out some french phrase...