VoIP Communication Management - Why Call Accounting Is Regaining Killer Application Status
Companies that have relied on call accounting software to provide system metrics from their traditional PBXs are demanding more encompassing solutions to bridge their PSTN and VoIP implementations. Improperly managed VoIP networks can succumb to new threats such as denial of service (DoS) attacks, hackers, viruses and spamming.
Source: ezinearticles.com

VoIP PBX Telephone Systems & The Advantages
The most important plus of VoIP PBX is that it is many times easier to install and configure than a traditional phone system. Any one who knows the basics of computer and networking can install the IP PBX in a PC and maintain it reasonably well. Also, since it is all software, there is no complex wiring involved anywhere.
Source: ezinearticles.com