In the previous company I worked for, Instant Messaging was an integral part of office communication. Situated somewhere between a phone call and and email, one could quickly get information from someone without the full disturbance a phone call incurs and the long response times and explanations in an email. Moderate use of course was highly recommended and by and large it worked exceptionable well.
For two years now, however, I have to do without it as my current employer does have an Instant Messaging applications as part of its supported IT infrastructure and third party software is not allowed to be installed on the computer. And even after two years I miss it as a tool. Often, I don't want to call someone unless absolutely necessary but an eMail is too slow so I end up calling. Not very efficient.
Perhaps Instant Messaging on smartphones would be an alternative as most people in my environment are always-on these days anyway. Even critical mass might not be too hard to reach as Google Talk on Android phones gets activated by default anyway. But then the solution would lack the ease of a real keyboard thus making it clunky to use for most people. Also, exchanging company information over an unsecured channel is not the right thing to do.