T-Mobile devices have a default Wi-Fi Calling feature that keeps you connected in areas with little or no coverage using Wi-fi connection. But according to new finding by studentsandfromthat this feature lets millions of Android users vulnerable to Man-in-the-middle attack. The flaw could potentially allow hackers to access and modify calls and messages made by T-mobile users on certain Android smartphones on certain phones. The simplest way to become a man-in the middle would be for the attacker to be on the same open wireless network as the victim, such as at a coffee shop or other public space.
Source: https://thehackernews.com/2013/03/t-mobile-wi-fi-calling-app-vulnerable.html