Twitter: Discussion

After I used twitter, I feel it almost looks like text messages. The difference is text messages can only send to one person at a time and only view by the receiver. But with twitter, your message can be view by a bunch of people, especially those who follows you with just one click and it is for free. I think I'll ask my friend, who serves in Iraq right now, to join twitter. So she can updates her status regularly, and her family or friends will know how she is doing over there.
How does twitter discussion compare to Bb discussion? To an in-class discussion?
The similarity between twitter and Bb discussion is both of them allows only register users to reply to the posts. However, the posts in Bb discussion are more private, in which some of the Bb sites only allows register users to enter and view the posts. While twitter allows everyone to find and view the posts. The replies in Bb discussion are more organized than twitter because you cant find replies underneath your posts in twitter. The difference between twitter and in-class discussion is that you can hear instant reply from the classmates in in-class discussion. While with twitter, other users must log in and views your tweets and then reply.