Sling TV, Dish's internet TV service, is seeing steady growth according to numbers published by The Wall Street Journal. There are currently over 600,000 monthly subscribers, according to "people briefed on the numbers" who revealed them to the Journal. Back in November, an analyst estimated that Sling had "at least" 394,000 customers paying $20 per month for Sling's package of channels including ESPN, Disney Channel, AMC, TNT, TBS, CNN, and others. Since launching just over a year ago, Sling TV has added more paid add-on packages — each offering more channels — and also now lets users subscribe to HBO and Cinemax.

Sling's inexpensive (compared with traditional cable) watch-on-any-device skinny bundle was designed to appeal to millennials and consumers who've so far resisted bringing Comcast, Time Warner Cable, or Dish itself into their homes. Access to ESPN is seen as the product's best selling point, and the sports network seems happy with the new viewers it's bringing in. "We've had a good uptake on that product," ESPN president John Skipper told Recode's Peter Kafka at this week's Code Media conference. "That product has brought in new people to the pay television universe. ESPN is the driver of that package."

"Our concern is whether or not we're getting new subscribers or are we getting subscribers trading down from an existing package? What we have learned from meeting with Sling is that the vast majority of those subscribers are incremental, so we are much more bullish now about the opportunity to push further," Skipper added.

This year, Sling TV plans to roll out an updated, far sleeker, and more intuitive user interface. The update, which also adds ESPN3 to the core channel pack, will debut on set-top boxes before moving to mobile devices. Sling TV hasn't yet confirmed the subscription figures reported by the Journal. At least for right now, the company isn't facing a ton of other web TV competition; Apple has reportedly put its plans for a streaming video service on indefinite hold, and Sony's PlayStation Vue has seen a much slower rollout since it also offers local networks like Fox, NBC, CBS, and ABC. Comcast is making moves to attract cord cutters with internet-only TV, however, and ESPN's Skipper hinted that other services are likely to launch this calendar year. But Sling's off to a decent — if unexceptional — start.