There should a 'Buzz' for alert
There should be a 'Buzz' to alert the other user. Like, Spark, Yahoo.
Sometimes we have messaged to another user. But user is busy on another task. He/She missed the messages which is very important.
In this case, the user should have a 'Buzz' button or shortcut for alert to someone. I hope everyone knows about the importance of 'Buzz'. :)