Google's MVNO cell phone service, Google Fi, is getting a surprise new feature: encrypted phone calls. Encrypted voice chats via messaging apps have been available for a while, but this is the first time we've seen a company hijack the regular phone system for end-to-end encrypted calls. Open the phone app, dial a number, and your call can be encrypted.

End-to-end encryption is not a normal phone standard, so both parties on the call will need to be firmly in the Google Fi ecosystem for the feature to work. Google's description says that "calls between two Android phones on Fi will be secured with end-to-end encryption by default." Google Fi works on the iPhone, too, but given that Google would have to use Apple's default phone app, it can't add encryption.

For encrypted Fi-to-Fi calls, Google will show a new "Encrypted by Google Fi" message in both users' phone apps, along with the ubiquitous lock icon. The company says there will be "unique audio cues" as well.

Google doesn't explain how the encryption works, but presumably, the feature is tacked on to Wi-Fi or VoLTE (Voice over LTE) calls. It would be tough to do this over traditional voice networks, but if you're running the voice call over data and control both client apps, wrapping the whole session in encryption becomes a lot easier. I wonder if encrypted calls will be billed as Fi's metered data usage rather than unlimited call minutes.

Google says the feature will roll out to Android devices "in the coming weeks."