In the elementary school you can help kids build reading comprehension with their reading. Encouraging students to go on IM and find a friend in another classroom or another school to have a book talk with. They can have list of questions and ideas to share to encourage higher level thinking.
While IMing students tend to use shorter sentences and are more likely to make a mistake on their spelling... Print off past IM conversations that they have had and have the students use their own words to edit and make revisions.
There are different games students can play using IM. They can play word association games with people in the other classes. They can be given a simple sentence and work to compete who can make it more elaborative. Students can be working in groups comparing skills being taught in one class to another. They can work in teams share information about the location they are at and compare to where the other team is (this would be great if they were in other states or even countries).
IMing can go beyond the typing and use videos to chat from one location to the next.
Students in one class could be responsible for part of the morning news.
Older students can read to younger students. This would also be great for ELL students to have someone read to them.
Using the video chatting would be great to use when someone is absent. This would not replace the importance of in-class learning but this would be a great way to keep someone connected if they were out for a long time.
Bringing IM into the classroom is a new way of using communication that makes us all stretch our thinking outside the box or should I say wall of our own classroom. :)