Johna Till Johnson, president of Nemertes Research LLC in New York, said 31 of 50 large companies she surveyed this year reported that they're using VoIP technology.

"Effective cost-justification is a major challenge," Johnson said. But the survey showed that VoIP systems are about 22% less expensive to operate than circuit-switched networks, she said, adding that her research wasn't sponsored by any IT vendors.

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