Jott has a lot of free services. I used to pay for the services (until I got my itouch and it does many of these things) but it is great for those who travel a lot or who type slowly and away from the computer a lot.
Set up free conference calls and allows as many people as you like to set up and participate in the conference call. Many of us use skype, however, if you go over 10, and people are just in the US, you could use this instead.
The great things is that this gives you recording of the conference with no time limit. The MP3 file is given to the host.
This one is from Liz Kolb and is a site that allows you to have extra management features for your email including translating the messages into text. You can create multiple voicemails and greet students and others by name (it reads off caller id.)
You can have students call and leave a message for you as their assignment. It converts to an mp3 for you. Could also use for something like radio call in show, and pull Mp3 files off and then turn into a podcast by remixing in audacity.
So, if you want twitter to automatically tweet (like when your class blog is updated,) then set up twitter feed to automatically post anything to twitter that has an RSS feed. I do this for my classroom to send my blog or any current information that students need to have.