Just like O2 users in the UK, now Movistar users in Argentina, Colombia and Peru and Vivo users in Brazil are able to use the TU Go app to make Wi-fi calls to avoid roaming charges or when they are in an area where carrier signal does not work well.
The app allows the user to use their carrier minutes and texts over any data network, in any part of the world, without paying any extra taxes. It works just like if you were calling from home on a regular cellular device.
It is possible to set up to 6 devices with the same phone number, and it syncs up with your device contacts and combines call history and messages across devices too.
Plus, you can install it on a desktop running Windows 7 or later, or even use the service in a web browser.
Find the app in the Windows Store here.