Comcast Corp. is entering the fiercely competitive wireless phone market, just as big carriers like AT&T Inc. and Verizon Communications Inc. are pushing unlimited data plans and jockeying for a piece of Comcast’s television turf.

The nation’s largest cable-TV company by subscribers unveiled Thursday details of a service, dubbed Xfinity Mobile, that it has been preparing to launch for years. The service will be available to customers only in combination with at least the company’s home internet service.

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