Tariffs are not transparent. In my case, I was booked into a pay-as-you-go tariff called "Talkalot" and although I didn't use my o2-number for outgoing phone-calls or data they sent me a lot of stupid messages about roaming and new tariffs. But what was even more annoying: Although I didn't use this number for any outgoing calls or messages, o2 informed me regularly about my account and charged fees without telling me why. I guess I had to pay for these tumb adverts sent as text messages. I will no more use any "service" from o2 and changed already my provider. Criminals like these ones will not be supported by me!