The service allows you finding out who has called you, when the telephone line was busy, switched off or was outside the zone of coverage. By doing so, it ensures that an important call will not be missed.
IDC projected over 9 billion minutes of voice traffic to travel over worldwide packet networks in 2000, exceeding 135 billion minutes in 2004. Service revenue is projected at 1.6 billion in 2000 and 18.7 billion in 2004.