Voice over IP is really a variety of services.
The vision of voice communications carried over a packet-switched data network is hypnotic, promising compelling services such as a single inbox for e-mail and voice mail, easy call transfer around the block or around the country, user-controlled feature changes and simple remote systems management.
Often used as a catch-bin label, VoIP actually refers to a number of completely different approaches. The most basic system uses two or more on-site VoIP switches with a digital network connection running between them. Functioning like a Private Branch Exchange (PBX) and supporting standard phones and phone lines inside the company, these switches take internal phone calls, dice them into packets and ship them over a digital connection to the other VoIP switch, where the packets are decoded back into analog voice. Some existing analog PBXs can be upgraded to support such point-to-point VoIP phone calls.
Things gets more interesting when merging separate voice and data networks into one. You can then attach "smart phones," each with their own IP address, to the data network in a corporate office. These so-called IP telephony systems meld voice mail and e-mail into one, allowing voice and data messages to be forwarded around the network with ease. Traditional phones and phone networks disappear, along with their separate wiring and proprietary hardware. Each phone can be configured to provide customized services such as easily changing voice-mail prompts, and remote management becomes far more cost-effective.
VoIP can also be used in the phone system fabric. Some telcos will take a VoIP call from a user's switch and continue to transmit it as IP packets deep into their own network. Because it can be more cost-effective for the carrier, the cost of such phone service is coming down.
The full value of VoIP will come when every employee in the companyand the people at other companies they want to callare all using smart phones, and the phone carriers can transmit all the calls as IP connections from one end of the call to the other. That will allow everyone to enjoy data-enabled calling features such as phone-based instant messaging and easy portability. But that day is still far in the future.
Ask your in-house networking guru:
What would it take to upgrade our network to support VoIP?
Ask VoIP equipment vendors:
How can I currently support VoIP at the lowest possible cost?
Ask your voice carriers:
What kind of services would you offer if I could bring you my voice calls as IP?