Internet telephony, which uses the Internet to carry voice and data, is still youthful, but the industry is growing — and gaining more users all the time.

For evidence of the industry’s health, attendance figures for the Internet Telephony Conference & Expo, set for Oct. 10-13 at the San Diego Convention Center, should suffice.

Rich Tehrani, conference chairman, said he’s expecting about 9,000 attendees and 250 exhibitors, numbers that should make the event the largest in the industry this year.

“This event will focus on the move of communications to Internet protocol,” Tehrani added. “Just as Web browsing revolutionized shopping, so, too, IP (Internet protocol) is revolutionizing communications.”

At least five local firms involved in Internet telephony are exhibiting.

“This is the fourth time that we’ve been to this show,” said Todd Benjamin, president of Rodopi Software, which makes software used for IP services. “It’s in our own back yard, and we’ve been able to pick up business both from people attending the show and from other exhibitors.”

Rodopi, named for a mountain range in Bulgaria, saw its sales double in the past three years as more consumers and businesses shift to IP-based networks from more traditional land-line phones.

“The quality is increasing, and the price is decreasing, as more and more people are getting broadband connections to their homes,” Benjamin said.

Tehrani said escalating costs with traditional telephone networks is driving many customers to Internet-based technology.

“Using technology based on the Internet is cheaper than the proprietary equipment of the old days,” he said. “Most consumers can save at least 30 percent, and if you’re doing a lot of international calling, you can save even more.”

Of course, as with any new technology, there are glitches, but the quality is always getting better, insisted Tehrani.

“The technology is not perfect, but every year we see it growing and every year we see it improving.”

Admittedly, Internet telephony is still in its early adapter phase, with only 5 million paid users in this country, Tehrani said. Yet when talking about all users, both paid and unpaid around the world, the number rises to more than 100 million, he said.