Nortel Networks Corp., the Canadian maker of telecom equipment, filed a lawsuit on Friday against Vonage - claiming that it violated nine patents related to Internet phone services and related features such as 911 and 411 calling and click to call. Nortel spokesman Mohammed Nakhooda said the lawsuit, filed in U.S. District Court in Delaware, countered claims made by Vonage that Nortel had violated three of its patents. Vonage Holdings Corp., Holmdel, N.J., was dragged into the legal battle after it acquired three patents from Digital Packet Licensing last year, according to Vonage spokesman Charles Sahner.