We are waiting for T-Mobile to update their ROM to include apps2SD. The international version, as well as the versions put out by other carriers, have this new, updated feature. Wi-fi calling is a T-Mobile US feature, so flashing the international ROM will remove it. T-Mobile is dragging their feet, and developers can't create custom TouchWiz ROMs that include wi-fil calling and apps2SD until T-Mobile issues their version of the ROM.
For now, we either have to wait or flash the international ROM, giving up wifi calling.