On the same day, Klausner Technologies Inc announced it had filed suit against Vonage for alleged patent infringement and was seeking and royalties worth $180m.

Klausner said Vonage’s voicemail services infringed one of its patents, which it currently collects royalties for from companies including Time Warner Inc subsidiary AOL.

For Vonage, it’s the just the latest in a series of IP lawsuits against the company. Notably, Sprint Communications LP sued Vonage last October for alleged IP infringement. Then in June, Verizon Communications Inc filed suit against the company for allegedly infringing at least seven of its VoIP-related patents.

Vonage does not believe it is infringing on Verizon’s patents. Furthermore, we feel that we have meritorious defenses to all of claims being asserted against us in this litigation, said a Vonage spokesperson via email.

After careful analysis and review, we are of the opinion that besides the lack of infringement, some of the patents being asserted against us are invalid and other patents are not even directed toward our technology

Vonage said it hopes to stem the legal tide by purchasing three VoIP-related patents from US holding company Digital Packet Licensing Inc. The patents relate to the compression of packetized digital signals commonly used in VoIP, Vonage said.

Vonage has acquired important patents in the field of VoIP technology in order to bolster its defenses against infringement lawsuits such as those recently filed by Verizon and Sprint, said the Vonage spokesperson.

We believe that the strategic acquisition of the Digital Packet patents will enhance our legal defenses and help quell the filing of frivolous lawsuits and attempts by others to discredit our technology. By acquiring the Digital Packets patents, Vonage has now gained additional resources to defend against infringement claims on its VoIP technology.

Holmdel, New Jersey-based said the three significant patents also places the company in control of pending litigation against Sprint, Verizon and others in federal court for infringement of one of these VoIP patents.

What’s more, Vonage said it was currently in cross-licensing negotiations with regard to patents with unidentified rivals. Already, Motorola, Time Warner, Qwest Communications and others have already settled with or taken a license from Digital Packet on the patents that Vonage has bought, Vonage said. Vonage now assumes ownership and control over these agreements.

But the company made no mention of Klausner’s suit. Klausner approached Vonage in January and asked it to enter into a licensing agreement that would have let it continue providing its VoIP voicemail, said founder Judah Klausner, in a statement.

We have already granted a license under the same patents to Time Warner’s AOL and are unable to wait any longer for a response from Vonage, Klausner said. While the AOL settlement amount was not announced, it was rumored to be for $200m.

For money-losing Vonage, the latest lawsuit adds to its mounting woes. The company saw its IPO in late May flop. Some say it’s the worst IPO Wall Street has seen so far this year. And its share price has slid since. A series of class-action lawsuits over the way Vonage handled its unusual customer share purchase program at the time of the IPO have also been filed against the company.

Vonage shares fell more than 3.5% to $7.40 on the New York Stock Exchange following the announcements.