Cablevision has extended its digital voice-over-cable telephony service across its footprint of nearly 4 million homes in the New York metropolitan area. Cablevision's Optimum Voice service was introduced on a trial basis earlier this year and officially launched throughout Long Island in late September. The service provides unlimited local, regional and long-distance calling across the U.S. and Canada for a flat rate of $34.95 per month. It includes five custom calling features (Caller ID, Call waiting, Call return, three-way calling and Call...