http://ec.europa.eu/information_soci...ta_roaming.pdf - the document I was referring to earlier. It is from 2008-06-24 so some of the information may be inaccurate but the gist of it still holds true. Most of that document can apply outside the EU as well.
(For instance, T-Mobile USA has few options for roamers besides unlimited BlackBerry e-mail for $19.99/month prorated, & their standard per KB charges of 1 cent per KB in Canada & 1.5 cents everywhere else outside the US & Canada. AT&T, on the other hand, is more complicated but offers some cheaper options compared to T-Mobile - which sounds strange given that T-Mobile is present in several countries - for travellers going to many, but not all, countries. The very cheapest still works out to $0.99995/MB & that's only if the entire 200 MB bundle is used & the highest rates are of course their standard rate of 1.95 cents per KB.)
PS: Can a moderator merge this post with my initial one in this thread?