The international talk and text add-on only comes into play when you are making calls from the U.S. [Or via wifi when overseas if your phone has TM's wifi calling feature.] It allows you to call certain countries for "free" or in some cases, a reduced rate.
The Simple Choice (postpaid) plan "works" in the countries you mentioned. When on a cell tower, outgoing is 20¢/min. to all 100+ Global roaming countries and back to U.S. Incoming will also be 20¢/min.