Stealth Communications, a New York City ISP, is offering a free service that allows carriers and enterprises to register their telephone numbers with an emerging directory service that enables VoIP calls.

Stealth late April announced that it was offering a free service that supports Enum. Enum is a network protocol that allows an end user to type a telephone number into a Web browser and access a URL listing the available Internet resources for that number, such as an IP telephony address, e-mail address or Web address. Enum is considered a key translation mechanism between the Public Switched Telephone Network and the Internet for VoIP applications.

So far, Stealth has signed up 12 organizations for its Enum registration service including VoIP service providers Packet8, Net2phone, China Telecom and 3U Telecom. Enterprise participants include MIT and Yale University.

"We've had people joining our Enum service over the last six months," says Shrihari Pandit, CEO and founder of Stealth Communications. "When we unveiled our service we had 1 million numbers."

Stealth's Enum service allows enterprises that are already running VoIP applications to have direct communications with each other over the Internet without having their calls routed over the PSTN. Today, many VoIP calls end up going over the PSTN when they're transferred between service providers. If ISPs use Stealth's Enum service, they can hand off calls directly and eliminate the portion of the call that would otherwise go over the PSTN.

"Our implementation of Enum will help those carriers and enterprises deploying VoIP to reduce their termination costs dramatically," Pandit says. "They all want to interconnect with each other to move off the PSTN and move onto the Web....Enum helps cut the PSTN portion out of calls while improving quality and lowering costs."

Enterprises with VoIP systems will need to enter all of their telephone numbers and contact information into Stealth's Enum service. Enterprises can then set up their VoIP systems to automatically check to see if a telephone number being dialed is entered into the Enum service and can be routed as a pure Internet call.

Pandit says the Enum service will not slow down call completion. "We should be just as fast as the PSTN," he says.