Not only is cable phone service cheaper that ILEC offerings, it sounds better and is more reliable, too. At least that's the conclusion of a study released this week by IP service test player Keynote Systems Inc. During tests in New York and San Francisco during August, Keystone found the quality of cable IP phone service exceeded that of the PSTN, not to mention pure-play VOIP services.

Keystone benchmarked the service offerings of several different VOIP providers, as well as traditional ILEC circuit-switched voice offerings. Of all the services tested, the digital phone offerings of MSOs topped the list for both service reliability and audio clarity.

This means that Comcast beat out AT&T in the Bay Area, while Time Warner Cable topped Verizon in the Big Apple. The MSOs also outperformed standalone VOIP players like Lingo, Packet8, Skype, and Vonage.

Keystone calculated the reliability scores with performance measurements in three categories: service availability, average number of dial attempts, and dropped calls. Call quality was calculated in terms of audio responsiveness (a measure of audio delay) and audio clarity (measured by Mean Opinion Score).

Interestingly, the study also tested whether "over-the-top" VOIP services like Vonage and Skype performed better over cable modem or DSL links. Telcos have long argued that since cable modem users share last-mile bandwidth, they are more likely to experience degradation in service quality than DSL customers. Keystone found otherwise. According to the Keystone release:

It had been thought that cable modem subscribers would suffer overall service degradation during peak hours (8:00 PM-1:00 AM EDT). However, the study revealed that while cable modem subscribers did experience greater instances of audio delay during peak hours, audio clarity (as measured by Mean Opinion Score) was not affected by the increased traffic associated with peak hours. DSL connections, on the other hand, were found to deliver more consistent peak versus non-peak audio delay performance, but were less consistent as measured by MOS.

North American MSOs added a record-setting 1 million IP phone customers in the second quarter (see Cable Racks Up Over 1 Million VOIP Subs in Q2 ). Increasingly, with cable phone, consumers are buying for quality, not just price.

- Michael Harris, Chief Analyst, Cable Digital News