Source: Matthew Miller via Twitter
As seen in the screenshot above, Wi-Fi calling is now a selectable option for T-Mobile iPhones running Apple's latest iOS 8 beta 3 software that was released alongside a new OS X 10.10 Yosemite developer preview build earlier today.
The addition comes one month after T-Mobile chief marketing officer Mike Sievert said the feature would be supported in Apple's final iOS 8 build. Canadian cellular provider Rogers Wireless also announced its network will be compatible with iOS 8's Wi-Fi calling function on rollout.
Like other carriers' Wi-Fi voice calling solutions, T-Mobile's version offloads incoming and outgoing calls to a local wireless network, offering a more reliable and stable connection as well as enhanced audio quality and better battery performance. As a plus, Wi-Fi calling takes load off the cellular network backbone and can help ease bandwidth issues in congested areas.
Under current terms, T-Mobile subscribers are allowed to connect to and make calls from Wi-Fi networks as part of their monthly subscription, though usage counts against plan messaging and minutes.
When Apple's iOS 8 debuts this fall, over 90 percent of T-Mobile's smartphone offerings will support the feature first rolled out with select Android and Windows devices in 2007.