One easy way to do this, is to record podcasts for your class announcements and weekly wrap-ups. My new favorite free podcast tool is called "Cinch". You can create an account at http://cinch.fm. What's great about Cinch is that you can create a different folder for each of your classes. You can record from your computer, OR make a phone call! You can even record and manage the podcasts with their Iphone App. It works like Twitter, and you can place a 'feed' on your Moodle coursepages, so students can easily listen to your last podcasts.
This is how it looks on our coursepages! (see left side)