Well, this is typical for people who are not insider or lets say "freaks" like us but normal users
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These flat-rates are only for the mobile browser and the operators detect which engine you use or force special proxy servers. We have such flat rates here from o2 (surf&mail) and also from vodafone. Also there people tried to use the laptop - which works with some tricks - and some got the several thousand euro bills afterwards as they were charged with the regular 19euro/mb standard tariff.
lovely.
Chris