The only sure way to ensure that you aren;t hit with unexpected bills is to also disable Cellular Data. I've done this overseas on several occasions (Europe, Asia) and I've never had a roaming data charge. If you're extra paranoid and are in a country that doesn't use 3G for voice you can disable...

Another app I've found really handy is CardSnap for iOS. It scans business card, sends them to a  cloud OCR service and then returns them into my address book. I reviewed it a while ago at my blog