For me, i have att, i can use my sim with att over seas it just cost a lot more (unless you are a special plan) so when i go over seas, i take out my sim and buy a local sim and use it instead. It depends on where you go, if thats cheaper or not.
As long as you have wifi access you should be able to use both apps, trust me you dont want to do "data roaming" on att while overseas you will be screwed. So i dont use att data overseas i take out my sim when i arrive.