Just moved Switzerland for 4-months with a new Blackberry 9300 Curve. I travel intl a lot and happily use and pay for the $20 Unltd Intl Bberry Email Service on Tmobile.

But now I'd like to turn all other data off, esp after accruing $50 in fees after my first week here. Seems like when you switch the data off on the new phone it cuts off email access too. Is this true?

I get lots of work email and need to read and reply to it freq, so turning off email is not an option. I seldomly use 3rd party apps and when i do it's only FB, Twitter, Google, and Google Maps. Nothing else. And I try to use free wifi connections when possible.

But what's the best way to manage the data usage so that I'm not spending a fortune? Do I have to customize/block data settings for all third party applications? Are there pre-loaded apps using data that I don’t know about? Any tips to keep the costs down are appreciated. Thanks!

Yes, if you turn off data, that turns of email as well. Email uses data.

Facebook and Google Maps use a lot of data. If you are concerned about data usage, be 100% sure that you are closing those applications and not leaving them running in the background.

I'm not aware of any selective way to block data usage for third party applications other than to delete them from the device.

Check this thread:
Blackberry in Afghanistan experiences anyone?

YMMV.