1) Vocaroo and Podomatic are both super easy to use; however, Podomatic required many more steps. If all I wanted was an audio recording, I would choose Vocaroo, rather than Podomatic in order to save time. Podomatic, on the other hand, offers the availability to upload photos, etc., giving me more control in how my final podcast functions. If it would benefit my podcast to have visuals, I would use Podomatic. Both are, as I said earlier, very easy to use, so I could see myself using either tool.
2) A podcast could be very helpful in communication within a classroom in a number of ways. It could be extremely valuable to a substitute. For example, the sub could listen to step by step instructions for finding something for class while actually finding it rather than having to keep looking at typed or hand-written instructions.
Also, parents and students alike could listen to (or view) podcasts through a class blog, etc., for information on what is happening in class. This is more effective than the newsletter idea, because it prevents the newsletter from getting lost on the way home.
A podcast would also be a great way to teach a lesson if a sub was not prepared. Rather than leaving the sub with a list of instructions for an alternative lesson, I could record my instruction (that a sub may not feel comfortable teaching), and students could listen to it in class. I could also record classes so that absent students have an easy way to catch up on what they missed.
Podcasts have lots of potential uses, depending on the imagination of the person using them to benefit communication.