That means that your smartphone will be able to make calls and send texts over a Wi-Fi network.
As such, if you’re at home without a good cellular network signal, you’ll still be able to keep in touch with contacts over Wi-Fi.
EE is currently the only network to offer the service in the UK.
“We’re proud to bring this new service to HTC One M9 customers, helping them to stay connected wherever they are,” says Peter Frolund, HTC GM for UK and Ireland.
The feature is currently rolling out to EE customers with HTC One M9 handsets today.
If you’re an owner of HTC’s latest flagship, head to your settings menu to check for the latest software update.
“Wi-Fi calls are seamlessly integrated into general usage, and are therefore indistinguishable from regular calls from an HTC handset,” explains EE. “Wi-Fi Calling from EE and HTC uses the phone’s normal dialler and contacts book to make calls, and the normal text button to send text messages.”
It continues: “Customers don’t need a standalone app, a unique HTC interface will automatically detect whether to use Wi-Fi or cellular each time the HTC One M9 is used to make a call.”
Related: Android M features: What's new?
It’s not clear which handsets are next in line to receive the update, but we’ll keep you posted.
Check out our smartphone group test video below: