As reported by SlashGear today, video chat capability in Google's new Hangouts app for Android is disabled when connected to an AT&T cellular network — you're presented with a friendly message that "you must be on a Wi-Fi network to join a video call." The restriction seems to be limited to AT&T; a Verizon device we tested works just fine.

If the story rings a bell, it should: AT&T went through this last year when it briefly blocked customers not on one of its new Mobile Share plans from accessing FaceTime over cellular. At the time, AT&T rejected claims that the blockade violated FCC policies, arguing that the Commission's rules were designed specifically to prevent carriers from blocking the download of apps that compete with their own-branded services; FaceTime, which is built-in rather than downloaded, would be exempt from those rules (or so AT&T argued). Nevertheless, the carrier eventually relented, permitting non-Mobile Share users to get on FaceTime calls without needing to connect to Wi-Fi.

When asked about the situation with Hangouts today, AT&T refused to address the app specifically (emphasis ours):

All AT&T Mobility customers can use any video chat app over cellular that is not pre-loaded on their device, but which they download from the Internet. For video chat apps that come pre-loaded on devices, we offer all OS and device makers the ability for those apps to work over cellular for our customers who are on Mobile Share, Tiered and soon Unlimited plan customers who have LTE devices. It's up to each OS and device makers to enable their systems to allow pre-loaded video chat apps to work over cellular for our customers on those plans.

Regardless, the quote speaks volumes: AT&T seems to be saying that it would've "let" Hangout video chats function over cellular, had Google only asked. It's also taking the somewhat broad leap that Hangouts, which is an app downloaded from the Play Store, is still "pre-loaded" by virtue of the fact that it replaces an Android phone's in-built Google Talk app. Even more tellingly, Google's Hangouts app for iPhone — a download, not a pre-loaded app, of course — works just fine for video calling over cellular.

It's no secret that other pre-loaded apps do work on an AT&T cellular connection — FaceTime and BlackBerry 10's BBM, for instance. The exact requirements in order for AT&T to issue a green light are unclear, but approved apps seem to be "aware" of the data plan that a customer is on in order to determine whether to allow the call to proceed.

Still, the situation leaves us with more questions than answers. Why would Google choose to have a Nexus 4, which operates entirely outside of AT&T's sphere of influence, comply with this requirement and fail gracefully with a message that the user must be on Wi-Fi? And is the new Hangouts app, just released today, really "pre-loaded" in the traditional sense of the word?

If Google truly isn't cooperating with AT&T, that's the most worrisome possible scenario — it would suggest that AT&T is actively detecting the type of traffic coming out of an unlocked, unbranded device and making a decision to reject it. If Google is cooperating, of course, that's a huge concern in its own right.

We've reached out to Google for clarification.

Update: The original article didn't mention that video calls do work over AT&T cellular in the Hangouts app on iOS.