This is not new but I think it is a good reminder for people traveling oversea (during summer / holiday):
http://www.t-mobile.com/optional-services/roaming.html

Calling seems to always cost money but a few countries I checked, data and text are free/unlimited.

There was a catch for WiFi calling. See here:
http://www.fatwallet.com/forums/arcmessageview.php?catid=55&thre…