Facebook gave all U.S. users of Facebook’s Messenger app for iPhone the ability to call their friends for free last Wednesday. If you currently use Vonage you will understand this technology.

The new addition lets people make free calls using Voice Over IP (VoIP) services, which deliver the calls using WiFi instead of cell networks, the Verge reports. Free call services like Skype and Viber also use VoIP services for phone calls. The advantage, besides being free, is that it allows users with poor reception or stingy phone plans to call other VoIP users without sacrificing call quality or wasting minutes.