In order to examine how the library can use these tools, I think it is necessary to distinguish the differences and similarities of these tools.
All of these services have one thing in common. All of them are used to transmit information from one party to the other. They are forms of communication.
Nevertheless, each of these services are very different from one another.
Email was the first mode of instant communication through the web. It has been around for a long time and most of us are very familiar with it. It is such a popular form of communication nowadays that, in the office setting, for example, it has almost completely replaced traditional forms of communication like faxes, memos and even the telephone. It allows transmittal of relatively large documents and attachments instantly, and many work settings would be at a loss without this tool.
Instant messaging is relatively younger than email. The amount of information it transmits is smaller, even though it has ample capacity to send large amounts of information, but it is implied that the communicating parties using IM will have a more fluid interaction than with email. While communication through email is somewhat less fluid, instant messaging is intended for more active, conversation-like communication.
Short messaging services are the most recent innovation in instant communication. As the name implies, short messaging services send a limited amount of information between parties. its focus is in transmitting quickly synchronized, condensed information. I personally believe that the success that these services enjoy is more due to hype than any other factor, since, in reality, it really does not offer any advantages that email or instant messaging can't.
Libraries have used email for internal and external communication for a number of years already. employees communicate through email, and most libraries have email options to inform patrons about hold pickups, overdue notices, etc. Some other libraries have taken advantage of instant messaging as well to serve their public better by offering reference services and homework help. Twitter and other short messaging services are still to be adopted as a tool, but, just like email and IM's, it will be the public who, in due time, will determine if they want to use this form of communication as a library tool.