BOSTON - The true value of convergence won't be realized until self-contained corporate VoIP networks are linked in to the larger IP world through carriers, network professionals said at last week's Fall VON 2005 Conference & Expo .

Some of these professionals say they are interested in tying their converged networks directly in to carrier facilities through IP trunks that use Session Initiation Protocol for transport. That would give businesses more flexibility in provisioning voice/data lines to facilities, while opening the possibilities of more-advanced applications, said those at the show, which attracted more than 300 exhibitors, 7,600 attendees and keynote speakers from companies such as BellSouth, Skype and Vonage.

But such deployments are in their infancy, as large IP trunks in carrier networks are hard to find.

"SIP trunking holds a tremendous value for tying a bunch of small sites together transparently," says Arnold Solomon, IT architect for the Southern Company, which operates utilities Mississippi Power, Gulf Power and Georgia Power, and provides wireless network services in the Southeast.

Most companies, whether they run traditional or IP PBXs, must plug these boxes in to digital public switched telephone network (PSTN) circuits from phone companies to make calls to the outside world. Companies might be able to connect branch offices and even home workers in to a unified VoIP network, but the VoIP stops at the voice carrier, in most cases, as it's converted to digital TDM voice.

The alternative is plugging in to an IP voice circuit instead of a less-flexible digital voice trunk. Solomon says if IP-based trunks connected the Southern Company's hundreds of offices and facilities, the firm could more efficiently manage how it buys and uses voice services, rather than having to purchase a local T-1 digital PSTN trunk to each site.

But Solomon adds that his own company still has far to go in terms of converging its internal networks before linking to a carrier via IP. With a mostly TDM-based infrastructure of Siemens PBXs, Solomon says the Southern Company is just starting to move toward IP handsets and PBXs.

Another user further along in its convergence push also seeks to take the next step with IP trunking.