Well, thanks both. I'm not sure I'm going to touch the folders' settings but my question was not only due to the upcoming trip to France, but even to the situation in Italy, where I live. In fact, my carrier, H3G, is a 3g only carrier and has serious difficulties covering all areas. So customers are allowed to the so called national roaming on another network but, in this case, data bundles don't work and I have to pay. Since when I'm going during summer time there is no open wifi and I have to go on national roaming, I wanted to experiment a tight combination of firewall (great invention, isn't it?) and data limits on k9. I believe 51 kb exchanged are ok after all, cause the national roaming data tariff is 60 euro cents per megabyte, so let's assume it's tolerable even if for a few days.
In Paris it would be different but I'd like to use gtalk or sms sent via a voip client instead of using normal sms which are priced 30 euro cents each!
We'll see.