Now that Comcast's (NASDAQ:CMCSA) spurned bid for Walt Disney (NYSE:DIS) is little more than an unpleasant memory, the nation's largest cable operator has its sights set on another target: its own subscriber base. The company announced yesterday that it intends to aggressively roll out voice over Internet protocol (VoIP), and will offer the service to its entire territory of more than 40 million households within the next two years.

The relatively new technology allows for the transmission of voice communications over broadband Internet lines. Internet telephony is less expensive than traditional circuit-switch technology, and represents a distinct threat to Baby Bells such as BellSouth (NYSE:BLS), SBC Communications (NYSE:SBC), and Verizon (NYSE:VZ).

Comcast inherited 1.2 million traditional residential phone customers with the acquisition of AT&T Broadband in 2002, but has been slow to leverage that segment of the business. Rival Time Warner (NYSE:TWX) already offers VoIP to half of its 11 million subscribers, and 3,200 customers weekly are signing up for Cablevision's (NYSE:CVC) Optimum Voice service.

Comcast also announced plans to incorporate digital video recorder (DVR) functions into set-top boxes by year-end. The company test-marketed Tivo (NASDAQ:TIVO) several years ago, but will instead be using DVR technology developed by Scientific-Atlanta (NYSE:SFA) and Motorola (NYSE:MOT). Microsoft (NASDAQ:MSFT) will also have a stake in Comcast's digital television; its software will serve as the platform for movies on-demand and other interactive features.

Not only will the new telephony service be an earnings driver (the incremental costs of adding services to existing cable lines is small), but it should also slow the defections of cable subscribers to satellite providers such as DirecTV (NYSE:DTV) and EchoStar (NASDAQ:DISH). Customers who have integrated voice, video, and Internet services are more reluctant to switch providers. Of course, phone and satellite companies will become allied and offer their own bundled services, but for now cable companies have the upper hand.

With 21 million subscribers and a presence in 17 of the nation's top 20 markets, Comcast is the clear-cut leading cable operator, double the size of closest competitor Time Warner. The company's size and established base should be an asset going forward. Cross-marketing emergent new services to markets already penetrated will become vital, given the maturity and stagnant growth of the core cable industry. Yesterday's decision to finally move ahead with advanced services such as VoIP and DVR comes not a moment too soon.

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Fool contributor Nathan Slaughter owns none of the companies mentioned.