U.S. VoIP subscription rates grew 21 percent in the second quarter of 2006, according to a quarterly report issued by TeleGeography this week.

The second quarter update of the market research firm’s U.S. VoIP Report shows that service providers gained 1.23 million new VoIP subscribers in the second quarter. Although this is down from the growth rate of 28 percent recorded in the first quarter, it still shows the rapid growth of the U.S. VoIP subscriber base. It also shows that VoIP is eating into traditional phone service at a rapid rate.

Currently there are about 6.9 million VoIP subscribers in the U.S., an increase of 153 percent from the second quarter of 2005.

Leading the pack is Vonage (News - Alert), with 1.8 million subscribers, followed by Time Warner Cable, which has just under 1.6 million subscribers. According to the report, both companies have followed similar growth trajectories in recent quarters: Vonage added 243,000 VoIP lines in the second quarter, while Time Warner added 234,000 lines.

Cablevision remained the third largest VoIP service provider, with 987,542 subscribers, up from 865,000 at the end of the first quarter.

Comcast (News - Alert), a late-comer which entered the VoIP market by first tipping its toes in the water, has now gone full steam ahead, gaining 305,000 new VoIP customers in the second quarter, an increase of 73 percent over the first quarter. The service provider finished the first quarter with 721,000 VoIP customers. According to the TeleGeography report, Comcast is on track to overtake Cablevision as the third-largest VoIP provider in the fourth quarter.

For more information, visit www.telegeography.com/products/us_voip/index.php.

TeleGeography’s U.S. VoIP Research Service offers quarterly reports measuring market size, competition and consumer preferences. The service offers spreadsheets and analysis on revenues, market shares and forecasts.

For more information about TeleGeography, visit www.telegeography.com.

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Patrick Barnard is Associate Editor for TMCnet and a columnist covering the telecom industry. To see more of his articles, please visit Patrick Barnard’s columnist page.