T-Mobile USA today announced built-in Wi-Fi calling for a variety of Android-powered smartphones, including the recently announced new T-Mobile myTouch and Motorola Defy.

T-Mobile launched Wi-Fi calling on a few BlackBerry and Nokia devices back in June of 2007 and currently hosts about 40 million Wi-Fi calls per month.

“This new execution of Wi-Fi Calling technology helps us ensure that our customers’ Android-powered smartphones can keep them connected to the important people in their lives where they work, live or play,” said Torrie Dorrell, vice president, connected family products and services for T-Mobile USA, in a statement.

Powered by Kineto’s Smart Wi-Fi application, T-Mobile’s Wi-Fi Calling for Android smartphones will be ready to use out-of-the-box, providing the ability to make voice calls and send SMS from accessible Wi-Fi (802.11 b/g/n) access points across the globe in addition to the connectivity available through T-Mobile’s mobile network.

T-Mobile says Wi-Fi calling for Android will be available “in the coming months,” on select Android devices. Both the myTouch and Defy are expected to be available by the holidays.