TinyVox is an iPhone application that allows users to easily link to a recorded audio file to their Twitter, Facebook, and/or Tumblr feed. If you are using Twitter with your students then TinyVox would be a great way to provide students information via an audio recording. You could explain a homework assignment or project. You could easily record an extra credit assignment as well. Voice reminders work a lot better as well, so you could remind students to study or return a form the following morning.
When you complete your recording you can preview it so that you know it sounds like how you want it. You can also provide a title for it. You then easily can send it to your followers on Twitter. With TinyVox you will be able to easily save your recordings to review later or record several at one time and then send them when you are ready.