Facebook (NASDAQ:FB) is exploring its next big thing by launching a test of a voice over Internet Protocol system – with which users can place a call via Wi-Fi or cellular connection — in Canada. It’s integrated in the company’s Messenger app and is available on Apple (NASDAQ:AAPL) iOS devices

If the VoIP system gets traction, Facebook plans to roll it out to other countries and add it to Google’s (NASDAQ:GOOG) Android platform — a clear threat to traditional carriers like Verizon (NYSE:VZ) and AT&T (NYSE:T), as well as smaller operators like Vonage (NYSE:VG) and Microsoft’s (NASDAQ:MSFT) Skype.

After all, Facebook has more than 1 billion users who visit the site frequently, including strong adoption on mobile traction, as illustrated by Messenger’s 12th-place ranking in the App Store.

The caveat: VoIP uses data, which, depending on your data plan and whether you have Wi-Fi, might not actually make the service cheaper to use.