Next Up to Sue Vonage? AT&T

Battered and bruised from its patent fights with Sprint and Verizon over technologies used in its VoIP service, Vonage disclosed Friday that it has also been sued by AT&T.

The lawsuit was filed October 17 in US District Court for the Western District of Wisconsin. AT&T says Vonage is selling products that infringe on the company's patents surrounding 'packet-based telephony.'

AT&T further claims that it had attempted to enter into a licensing agreement through negotiations for the past two years, but failed to find a "mutually amicable" agreement between the two companies.

Sought is an injunction preventing future infringement, as well as unspecified damages and attorney's costs.

"The complaint relates to a single patent for a wide area packet telephony system," Vonage's SEC filing reads. "Although the Company intends to continue to pursue an amicable resolution of this matter, the Company cannot assure that this matter will not ultimately be litigated."

With this latest rush of bad news, Vonage shares have fallen even further towards penny stock territory. As of midday trading Monday, The stock was down another 8.4 percent to $1.41, heading towards its 52-week low of 89 cents set in late September.

Vonage managed to settle one of its legal problems so far. Earlier in the month, it announced a settlement with Sprint. However, it still is embroiled in a legal battle with Verizon, and has asked a court to review a ruling against it.