This application increases the probability of a call completion, since the caller knows the status of the other party, and can determine whether that person is available for a phone conversation, or whether the issue can be discussed via IM alone, avoiding the need for the call.
According to Forester Research, presence is dial-tone for people.
Think about it. The familiar hum we know so well is the network's way of saying it is available to handle the call. In presence applications, a person's presence is their way of saying that they can handle the Instant Message or in telephony presence management, on-hook indicates that they can handle the call.
It is truly amazing to me that through the wonders of IP networks can with so little effort indicate something as simple as knowing whether the called party is able to pick up when you call. In fact, it can be useful to know that they're on the phone.
Sometimes, it may help to go down to their office and visit them…. to make the offer or pose the question directly. But there are as well, other issues that need to be addressed.
Just last week, I was logged into my IP telephony account from my Rolling Meadows IL office. Friend asked me a question via email, and noticed my presence online. He immediately assumed that I was in my 'normal' office – Marlborough MA – and came down 2 floors to discover that I was in fact in Illinois, some 850 miles west.
Presence management will grow beyond simply online and offline (a la AIM) to telephony presence (on hook, off hook) and then to location services, where even the 911 or public safety professionals will know where you are physically. This is a problem with wireless operators too, as they are bound by FCC regulation to support or plan to support mechanisms to report a 911 caller's location.