Facebook today began testing a new feature in its Messenger app that lets Canadian users call each other for free anywhere they have a Wi-Fi or cellular data connection. The test for now only applies to Messenger for iOS, but could roll out to Android users, as well as people worldwide, if the test goes well. Those outside Canada will today receive an update on both Facebook Messenger for Android and iOS that lets users send each other short "push to talk" voice messages (pictured). While voice messages instantly put Messenger on par with popular apps Voxer and HeyTell, VoIP calling is a much bigger deal, and would have enormous ramifications if it were to roll out to all Facebook users.

It might not be long before Facebook's hundreds of millions of users can call each other over Wi-Fi for free

If the VoIP through Messenger testing goes well in Canada, it might not be long before Facebook's hundreds of millions of users can call each other over Wi-Fi for free. VoIP will also work over your phone's data network if you're out and about, and will use about as much data per minute as competitors Skype, Vonage, and Viber. The feature is especially valuable for those with bad cell service at home, or for those who want to save money on monthly cell phone plans. Data-based messaging services like WhatsApp have quickly proven their mettle as better and cheaper alternatives to traditional SMS services, and phone calls have long been due for a similar disruption.

Yes, you've been able to make free Skype, Vonage, or Viber calls over Wi-Fi and cellular data for some time, but far more people use Facebook than any of those services. Plus, Facebook Messenger has consistently hovered near the top of the Google Play Store and App Store, meaning many people already have the app installed on their phones. The key here is scale, and there's no doubt carriers will take notice — if the FaceTime wars are any indication, at least.

The biggest obstacles to gaining mass adoption will be convincing users to ditch their phone numbers and trust Facebook with their calls. But since they'll likely be saving money or improving the quality of their voice calls, it could be well worth it for many people. Once again, this is, like many of Facebook's tests, a probe into one of its smaller markets to gauge a reaction. If the reaction is good, we might soon see the rise of the world's largest network of free VoIP callers. At the very least, anyone with the Facebook app will now be able to send quick voice messages if they're in a basement (or CES hall) with Wi-Fi but no cell service.