Netflix has periodically opposed zero-rating schemes in which ISPs exempt certain online services from data caps. But the US' biggest online video streaming company was a launch partner for T-Mobile's Binge On video zero-rating program, and this week it explained why it thinks T-Mobile's zero-rating is good for customers and video providers.

Netflix CEO Reed Hastings was asked in an earnings call this week why Binge On is different from Comcast's implementations of zero-rating.

"It's voluntary on the customer. Any customer of T-Mobile's can decide to turn it on or turn it off—that would be a big difference," Hastings answered. "They're not charging any of the providers; it's an open program. Many of our competitors such as Hulu and HBO are in the program also."

Back in 2012, Hastings accused Comcast of "no longer following net neutrality principles" when the cable company exempted its Xfinity video app for the Xbox 360 from data caps, while counting Netflix, HBO, and Hulu usage against the cap. "Comcast should apply caps equally or not at all," Hastings said at the time. (Comcast just launched another in-home streaming service that also doesn't count against caps—Comcast says its own services are exempt because they travel over Comcast's private network instead of over the Internet.)

Netflix's uneasy feelings about data cap exemptions cropped up again in 2015 when the company struck zero-rating deals with Australian ISPs. (Netflix declined to say whether it had to pay for the data cap exemptions.) After receiving criticism, Netflix said it had made a mistake by participating in ISP programs that "effectively condone discrimination among video services" by capping some but not others.

"We should have avoided that and will avoid it going forward," Netflix said at the time.

Netflix also said then that "ISPs should provide great video for all services in a market and let consumers do the choosing." With Binge On, Hastings says T-Mobile is letting consumers do the choosing and that it's up to each video provider to join or not.

"That's a really unique program that T-Mobile has done, and it's seeing a great reception amongst our users and we're seeing viewing going up," he said. "We hope those kinds of programs expand."

Binge On throttles bandwidth of video streams and downloads to about 1.5Mbps, forcing video providers to lower streaming resolution to about 480p. The throttling affects nearly all video, even from video providers that haven't chosen to join the program. Though video providers don't have to pay to get into Binge On, they do need to meet some technical criteria to get their videos zero-rated.

480p, the equivalent of DVD quality, is still "very, very good" on a 4- or 5-inch smartphone screen, Hastings said.

Binge On is enabled by default, but consumers can turn it off. T-Mobile has been criticized by net neutrality advocates because Binge On is opt-out rather than opt-in, and it throttles video regardless of whether the provider gets a data cap exemption.

YouTube has said that while reducing data charges benefits users, "it doesn’t justify throttling all video services, especially without explicit user consent." The Electronic Frontier Foundation has accused T-Mobile of violating net neutrality rules. T-Mobile met with the Federal Communications Commission about Binge On, but there's reason to think the FCC won't find the carrier to be in violation of the rules. There's no explicit ban on zero-rating, and the opt-out nature of Binge On may prevent it from violating a no-throttling rule. When consumers opt out, all video is streamed at full quality and counts against high-speed data caps.

While T-Mobile gives out the data cap exemptions for free, Verizon Wireless just announced that it will sell data cap exemptions to content providers. Hastings said he doesn't yet know enough of the details about Verizon's program to comment on it. AT&T has been selling mobile data cap exemptions for two years, but Netflix hasn't forked over any money.