Cox is one of the nation's largest cable providers, with 6.2 million residential and commercial customers. Though it has offered fixed-line phone service since 1997, Cox does not have any mobile services today.

The company will partner with Sprint Nextel to quickly launch a 3G (third-generation) service next year, but it is also building out its own network for launch next year in some of the markets it serves, said Cox spokesman David Grabert. Overall, four markets will go live next year, he said. The company did not disclose those markets or dates for availability. The same features and services will be offered both in markets served directly by Cox and those in partnership with Sprint, Grabert said.

Cable operators are bundling services, including TV, broadband Internet, voice and mobile, to ultimately offer subscribers a one-stop shop and a single bill. They hope bundling also keeps customers more loyal.

By building a mobile network of its own, Cox is committing itself to an expensive and complex project that its rivals have left to partners already in the cellular business. Comcast, Time-Warner Cable and Bright House Networks have joined with Sprint and Clearwire to help build out a national WiMax 4G (fourth-generation) mobile broadband network and plan to offer services on it.

Cox said it is building its own infrastructure so it can control the whole operation, including marketing, sales, back-office operations, customer support and billing. This will help the company maintain its strengths of network reliability and good customer service, according to Grabert.