Taking a different approach than the vast majority of the voice-over-IP market, Dialpad Communications today announced new unlimited, ultra-cheap voice service geared only at second line usage.

The DialpadUSA service, unveiled at the Consumer Electronics Show in Las Vegas, lets users make unlimited calls to the U.S. and Canada for $11.99 per month. Like most other VoIP services, the service comes with an in-home routing device that connects to the user’s broadband connection. However, instead of connecting directly to a phone, the device dubbed the dpPhone includes a separate jack for the PSTN line, allowing the user to stay connected to the public network.

All 10-digit calls are routed over Dialpad’s network while local, 911 and operator service calls, as well as any call made during power outages are routed over the existing ILEC connection.

And while most other VoIP providers are targeting primary line service, Dialpad CEO Craig Walker said the mass market still isn’t familiar enough with VoIP, and a little hesitant to dump their primary ILEC line.

“Most of the research we’ve done says people are using it for second line,” he said. “I think that’s still a little bit premature to say it has to be primary line. People like the security and safety of knowing that when the power goes out, you can still call the power company and let them know.”

Dialpad also is counting on the fact that most DSL users must maintain local service. Perhaps most significantly, the approach gives the company a differentiator among the hundreds of consumer VoIP players.

“We look at the captive group who are forced to keep the PSTN and the group that is treading lightly into this with a second line,” Walker said.