Comcast Corp.'s venture into the smart phone business is expected to run up about $1.2 billion in operating losses over its first 18 months of its existence, cable company executives say.

Launched in mid-2017, Xfinity Mobile ran up $480 million in red ink last year. Chief financial officer Mike Cavanaugh said that there could be an additional $200 million in losses in 2018, for a total of about $680 million, as Comcast boosts marketing and broadens the offering to include older smart phones that can connect on its wireless network.

Comcast broke out Xfinity Mobile's financial performance in its latest earnings report.

So far Xfinity Mobile has signed up 380,000 subscribers. It offers buy-by-the-gig data plans.

Comcast separately bought $1.7 billion in wireless spectrum in a government auction in 2017, though it currently resells Verizon wireless spectrum branded as Xfinity Mobile. Comcast said it will be be able to use the spectrum it bought from government for several years.

Xfinity Mobile is only available to Comcast TV or internet subscribers.