More than six months after launching their ZenKey app, the top three US mobile network operators don't have much to show for it.

When questioned about the app, an AT&T representative said the operator has been working with unnamed companies to test the offering. "We expect to have more news soon," the spokesperson said.

Moreover, few customers appear to be using the app. For example, AT&T's Android version of the app has been downloaded just a few hundred times, according to the Google Play store. And app monitoring company Sensor Tower shows fewer than 5,000 downloads for AT&T's iOS version of the app.

The T-Mobile and Verizon versions of the app show similar download figures.

ZenKey traces its origins to a 2017 announcement by AT&T, Verizon, Sprint and T-Mobile of a Mobile Authentication Taskforce that would "develop a mobile authentication solution for enterprises and customers." The initiative is basically a US version of the GSMA's "Mobile Connect" program for digital authentication.

The US Mobile Authentication Taskforce initially promised a service sometime in 2018 but ended up not launching the ZenKey app until late last year.

ZenKey is essentially a "single sign-on" (SSO) service from the country's top mobile network operators. Their goal is to get major online services like Amazon, Dropbox, Spotify and Netflix to use ZenKey instead of their own login and password systems. US operators argue ZenKey is more secure because it's backed up with their location and SIM data.

However, they're going up against established SSO offerings from the likes of Google and Facebook.

ZenKey's login services were publicly demonstrated last year with streaming music provider Slacker, financial company Fidelity and AT&T's DirecTV. However, AT&T is now moving away from its DirecTV service, and Slacker was acquired by LiveXLive, which is the company that also built the ZenKey app.

— Mike Dano, Editorial Director, 5G & Mobile Strategies, Light Reading | @mikeddano