The number of U.S. businesses using an Internet telephony line will surpass 5 million by the end of the decade and hit 7.8 million by the end of 2012, according to new projections from Pike & Fischer's Broadband Advisory Services.

In addition, providers of VoIP services will see revenues from business customers triple over the next five years to hit more than $6 billion, P&F says in the new report, VoIP in the Business World: Market Forecast and Analysis.

Businesses are increasingly attracted to VoIP services because of the operational efficiencies and cost savings. The biggest part of the market will be large enterprises, which tend to have in-house information technology experts to manage telecommunications upgrades, the Silver Spring-based market research firm says. Incumbent telephone companies such as AT&T and Verizon are likely to retain the biggest share of these customers, the report says.

Smaller companies have fewer built-in resources and may take a bit longer to adopt VoIP for their telecommunications systems, says Rich Power, a P&F contributing analyst and author of the report.

"The sales and marketing cycle may be a little longer for buyers in this segment," Power says. "There is just too much at stake to risk changes to their communications systems unless they fully understand the risks and potential rewards."

Nevertheless, the size of the market has attracted a number of new entrants who for the most part are doing a better job in selling to the small-business market, the report concludes.