Yahoo! Inc. today introduced VoIP in the United States. The company is positioning the service as an extension of its instant messaging service, Yahoo! Messenger.

Yahoo! is hedging its bets a bit by calling the rollout of Yahoo! Messenger With Voice a public beta test, even though the company has been offering many of the calling capabilities in international markets since December.

Yahoo! has split the service into Phone Out and Phone In. Phone Out allows consumers to make VoIP calls from their PCs to traditional or mobile phones in more than 180 countries; in the U.S. and in select other countries, the calls cost two cents a minute or less. Phone out lets consumers receive calls on their PC from traditional and mobile phones for $2.99 a month or $29.90 a year.

Yahoo! will make Messenger with Voice available to subscribers of its co-branded Internet access services, including AT&T Yahoo! High Speed Internet, in the coming months.

With the introduction, Yahoo! has beaten AOL to the punch. Analysts Richard Greenfield of Pali Research said he expects AOL to enter this market in the next six to eight weeks. Greenfield said he expects software-based VoIP services to become increasingly popular, especially with younger users, and that will put increasing price pressure on traditional carriers.

Falling prices will also put pressure on cable operators. According to Greenfield, “If services such as Yahoo Voice and Skype capture an increasing share of voice communication market share, with consumers increasingly expecting VoIP to be ‘free’ or nearly free, it will make it harder for cable industry investors to believe MSO VoIP price points anywhere near the current $30-$40 are sustainable.”