New InTouch app will be available to customers in August.
Three is following in the footsteps of EE by offering its customers the ability to make calls using Wi-Fi networks.
From August, Three customers will be able to sign up for the beta test of the operator's InTouch service, which will let them make calls as well as send and receive texts using a over a Wi-Fi connection.
However, Three's option will be app-based, as opposed to the native service announced last week by EE, which could mean a less seamless user experience when switching between networks.
The app, which uses the customers' usual Three phone number, utilises a customer's existing monthly allowance or prepaid credit for any minutes or texts used, with Three saying that it will particularly improve call quality in places where there is typically no mobile signal.
InTouch will be offered free of charge to all Three contract, SIM and Pay As You Go customers with devices running Android 4.0 or above, with the operator hoping to offer an iOS version upon full release later this year.
Three says that it's 3G network currently covers 98% of the UK population, and hopes to have its 4G network covering a similar proportion by December 2015. It currently carries 40% of the UK's total mobile data load, and plans to have 50 cities and 200 towns covered by its 4G services by December 2014.
EE announced last week that it would be launching a Wi-Fi calling service by next year, when it hopes its network will reach 90% of the UK population. The launch will come after the introduction of a VoLTE service, which the operator is currently trialling in rural Oxfordshire before going live later this year as part of a £275m investment in voice capabilities.
Earlier this year, the two networks announced they would be collaborating on a £1bn investment into telecoms infrastructure as part of a network-sharing deal to boost 4G LTE superfast mobile broadband for UK customers.
Source: Company Press Release