Short version: Install the free app Onavo on your iPhone or Android phone and get at least double from your expensive international data plan.
I travel quite a bit. About 2-3 times a year I go overseas - each time I experiment with different ways to stay connected.
International travelers: Please practice good data procedures. Your smartphone is a computer - with access to your passwords, photos and possibly banking information. Be sure to turn on any wipe/lock if lost features to your device! Also make sure you to reset your data before you leave, stay in airplane mode as much as possible, and turn data roaming off (until you need it) to minimize your costs.
I'm using ATT - their data plans are fair at best - and data is what I need the most when traveling. Google maps if neede. Maybe translation software. But it's $60 for 300mb (note - your ATT voicemails will ALWAYS come through a cellular signal.)
Onavo Extended it's a VPN (virtual private network) which routes all your data to their servers, where they dynamically recompress your data to get it smaller. It's going to slow down your data a little - but double/triple or more your data plan by compressing everything.
Start their app and it'll give you the ability to add a VPN to your device.
Once installed you can truly see what apps are taking up data (there's even a second app called Onavo Count to see that granularity.
Finally, when you get home, check your data usage (take screenshots just in case you need to prove it!) and uninstall/turn off Onavo.