In classic Un-carrier fashion meant to up-end Sprint's newly announced $50 unlimited iPhone 6-centric plan, T-Mobile has announced that it will start offering unlimited voice calls and text messages via Wi-Fi to all new and existing users.

T-Mobile's Un-carrier 7.0 event held in San Francisco on Wednesday saw its outspoken chief executive John Legere introduce Wi-Fi Unleashed, the company's new strategy for attracting new customers to switch over from their old mobile carriers.

"Wi-Fi Unleashed is a game-changer," says Legere. "This is like adding millions of towers to our network in a single day."  

While Wi-Fi calling is not new, with other carriers offering the feature in select phones since 2010, T-Mobile, however, is the first company to make the new technology widespread and easy to use for consumers. Traditionally, users have to set up a new app and get a special number to enable Wi-Fi calling. With Wi-Fi Unleashed, however, T-Mobile claims the device will seamlessly switch from T-Mobile's LTE network to any public or private Wi-Fi network in and out of the country and allow the user to make Wi-Fi calls and send messages using his own T-Mobile number, without having to install a new app.

T-Mobile says that all smartphones it sells from here on will come with Wi-Fi calling, and all existing Simple Choice personal plan customers will be able to receive an upgraded device if their current smartphones do not have Wi-Fi calling capabilities. Customers who wish to get a new device can do so through T-Mobile's Jump early upgrade program, which charges a $10 fee every month for the benefit of getting upgraded first.

To sweeten the deal, T-Mobile will also lend users a Personal CellSpot, which is basically an Asus router with 802.11 a/b/g/n/ac capabilities tweaked to prefer voice traffic over other kinds of traffic to ensure that users don't get their calls dropped when somebody else is trying to stream a Netflix movie from their Wi-Fi network. The Personal CellSpot is available for free but comes with a $25 refundable deposit, which the user gets back if he decides to return the router to T-Mobile. Customers will be able to get their own Personal CellSpot starting September 17.

Wi-Fi calls will also be available overseas and those Wi-Fi messages can be sent from 30,000 feet, as T-Mobile has partnered with in-flight Wi-Fi provider Gogo to allow users to send unlimited text, picture and voicemail messages onboard any plane that has a GoGo Wi-Fi network, which is around 70 percent of all airlines in the United States.

Wi-Fi Unleashed comes hot on the heels of a Google announcement that it is integrating its Google Voice voice-over IP (VoIP) calling service with Hangouts, which allows users in the United States and Canada to make unlimited VoIP calls via Hangouts free of charge.