Instant Messaging (IM) is a form of communication which requires an immediate response from the recipient. When you send an email message, it arrives in the recipient's account and when they choose, they can respond to it. When you use Instant Messaging, a box immediately appears on the recipients screen so that they can give an immediate response to your question. However, for IM to work effectively, the recipient must be logged on and present at his computer so GMS Instant Messaging provides you with a list of people who are available to communicate with.