AH, THE pleasure of phone tag. We call a colleague and leave a voicemail. Then we miss the return call, listen to the voicemail and jot down a note. It can take days before we get the information we need, and it's a horrible waste of time for everyone involved.
There's a simple way to test if your current communication methods are working: If you're reaching for a piece of paper, your communications process is broken. We shouldn't be jotting down voicemail notes and contact information in the 21st Century. To avoid this, we need realtime insight into where our colleagues are, understanding their availability and knowing how best to contact them at a particular time.
Communications become truly unified when you combine "presence - the ability to understand if a colleague is at his/her computer, in a meeting, on a conference call, or under a tight deadline and using that information to make contact in the most efficient way" - with a host of integrated workplace communications tools, including chat and video conferencing.