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In-Stat, a technology research company, released a report on Dec. 20 that noted an increase in voice-over-IP use in U.S. households.

The Scottsdale, Ariz., company’s newly launched residential VOIP tracker service showed more 9 nine million households have at least one active VOIP user while other households use more than one VOIP service.

According to the report, the top five facilities-based VOIP services used by households in the United States are Vonage (1.7 million households), Time Warner Digital Phone (1.6 million households), Comcast Digital Voice (1.3 million households), Cablevision/Optimum Voice (1.1 million households) and Cox Digital Phone (420,000 households).

Charles Gerlach, managing director of consulting at In-Stat, told eWEEK that “Adoption of both facilities-based and client-based VOIP services has been strong and consistent over recent quarters and we expect this trend to continue, fueled by continued activity on the part of the cable operators to market VOIP as part of their triple-play services as well as by the continued innovation and viral uptake of client-base services.”

The VOIP tracker service reported that the top five client-based VOIP service providers used by U.S. households are Skype (2.1 million households), MSN (1.1 million households), Yahoo Messenger with Voice (1 million households), Google Talk (658,000 households) and AOL Phoneline (266,000 households).

“Our research has consistently shown that the price savings is the biggest factor driving adoption of both facilities-based and client-based VOIP services,” Gerlach said in the same correspondence with eWEEK.

Gerlach reports that In-Stat’s research shows VOIP services are starting to lend themselves to business use as 46 percent of residential users currently use their VOIP service for business, which leads to an important question regarding VOIP’s future.

“Will the use of VOIP for business purposes at home translate into greater adoption in the business environment in the coming year?” Gerlach asked.

Gerlach said he believes the increase in VOIP use will continue as “we see no obvious barriers to significantly greater market penetration for both broad categories of VOIP services.”

Gerlach also said this year’s increase could lead to a few significant trends and questions regarding VOIP markets for 2007.

“In both the facilities-based and client-based VOIP markets, the most significant trends to watch will be the pricing and bundling strategies of the key participants,” Gerlach said. “How low will facilities-based VOIP prices go? Will innovative pricing schemes like SunRocket’s $199-per-year package continue to emerge and drive adoption? What will be the impact of Skype’s unlimited flat-fee North American SkypeOut calling plan on the market?”

No matter what trends or questions VOIP markets raise, Gerlach said use will continue to rise and added, “Users cite the fact that these types of services are easy and convenient to use and are also significant drivers of adoption as well.”