The broadband telephony market will swell to 28.4 million lines in 2013, an approximately twofold increase from 14.7 million subscribers last year, according to a report from JupiterResearch.

According to Government Technology, cable operators are expected to account for the bulk of the increase, as their voice-over-Internet protocol (VoIP) subscriber base is predicted to nearly double during the forecast period. Jupiter's report says cable multiple system operators (MSOs) have been able to remain competitive in the VoIP market by concentrating on triple-play service bundles. The report found that 47 percent of customers who subscribe to a cable MSO-managed VoIP service said that bundling was a key factor in their service selection.

"Broadband telephony enables fixed-service providers to integrate voice service features with other bundled services such as broadband, TV, or wireless," said David Schatsky, JupiterResearch president.