T-Mobile, which has supported Wi-Fi calling
for more than 17 million of its customers, has already confirmed that its iPhones will work with the built-in support for Wi-Fi calling coming in iOS 8 -- a new feature not mentioned on stage during the keynote, but one of many smaller features Apple is including in this fall's release. The OS-level support should mean that users will need only to tick a preference box to make the feature work.
Once iOS 8 is released, some 90 percent of all T-Mobile smartphones will have access to Wi-Fi calling, which can sometimes save voice and text plan minutes by automatically using public or home Wi-Fi when available. Up until today's announcement, only select Android and Windows phones were able to take advantage of the money-saving feature.
Among US carriers, Sprint also
has Wi-Fi calling -- but so far neither AT&T nor Verizon have announced support for it. Sprint is in the process of trying to merge
At any given month, according to the company, some five million customers take advantage of Wi-Fi calling. The service allows customers to use their cell phone to make calls even if local cellular service is poor or not available, as long as they can utilize a Wi-Fi hotspot. Caller ID and other features work exactly as though the phone was on cellular, but avoids roaming or long-distance charges, and recent-model smartphones (such as the iPhone 5 family) automatically switch over to Wi-Fi if available or if the cellular signal drops, without interrupting the call.
In addition to Wi-Fi calling -- which T-Mobile has supported in one form or another since 2007 -- the company is also expanding its existing HD Voice support, and recently launched its first public VoLTE
(Voice Over LTE) supported zone in Seattle, with plans for further national deployment over time.