No need for two threads for the same issue or question. >> Curve to Bold
You didn't mention which model curve you have. There are many and run different OS versions.
Don't know about the international calling, someone else will need to speak up about that. Regarding your data and apps, the data will likely transfer fine(make sure to do a backup and sync). However, the apps could get tricky. If an app is designed for a specific model phone and/or OS version, then it might not transfer and even it it does transfer, might cause compatibility issues.