Vonage is being sued for patent-infringement over its voicemail service for VoIP customers.

Klausner Technologies claims the company has infringed on its patents and wants $180 million in damages and royalties.

Klausner is one of a new breed of privately owned companies that does little more than protect the patent rights of their owner through lawsuits.

In this case, it is Judah Klausner who helped invent the PDA and electronic organiser and has a patent dating from 1994 that allows checking of analog voice mail from a remote location.

The company also controls another 25 patents on VoIP voicemail technology, and already collects licensing fees from Time Warner after it sued AOL for the same patent infringement in 2005, settling in April this year.

Klausner Technologies asked Vonage to sign a similar agreement in January, but the only response has been a request for more time, the company claims. Vonage has yet to respond to the situation.

It is the second patent infringement suit to hit Vonage in recent weeks. In June, Verizon claimed Vonage relies on seven of Verizon's patented technologies to make its VoIP system work.

Vonage, a relatively small company that went public in May, is fighting back with its own lawsuit. It is also getting into the patent game, announcing yesterday that it had acquired three VoIP patents from Digital Packet Licensing.

The new patents are unrelated to voicemail but they will allow Vonage to control licence agreements with competitors like Motorola, Time Warner and Qwest and to continue a federal patent infringement lawsuit against two other competitors, Sprint and Verizon.