I can't say that I totally believed the TM rep but when I went overseas earlier this year they said the international plan of 19.99 only covered email. Web browsing AND instant messaging (and they included BB messenger in there) were NOT covered. However, that's a TM rep...so you can never know for sure. Also, as Brian said above...some people browse the web, etc and never get charged...depends on how TM sees the 'data'. So you may get lucky.
'I am stuck on Blackberry and my Blackberry's stuck on me'