So, for a long time the most popular instant-messaging service used among inflation fans has been Yahoo Messenger. It kind of arrived at its status by default as most of the members who have been around for a while have YIM accounts, and newer members tend to create accounts on YIM since it was the most used service by those they wanted to RP with, and so the cycle continues. I know quite a few do have accounts on other services, or don't do instant messaging at all, but YIM is still far and away the most popular among those who do want to use instant messaging.