> Instant messaging applications enable communication that is online, synchronous and on-demand.
No. It's totally wrong. One needs to learn how to configure his chat tool that it doesn't disturb one in productive times, but is easily available when free. It's possible. I do it since ICQ. Unread chat messages will also still be unread if you continue to work 4 hours on your current task.
> Without [instant messaging], days are calm, purpose-driven and productive.
How can days be purpose driven if you don't sync your own work with your colleague's work any more? I'd argue that people who act like that are the least productive because they only work on things that are not valuable for the team at large.