Hi Marco,
I guess that Vodafone is happy with this to happen (not you, but your company... how much is 0.25 eur for 1000 people and for 1 million....)
I have found a way to prevent that your sim gets connected to the internet. Doing the below from the android manual.
¨ If the incorrect network or wrong APN settings are set, you will not be able to use the internet through the data network and so on.¨
So, I have added an APN to the vodafone's sim with wrong settings and assign the sim to it. Now your sim cannot connect to internet and Vodafone cannot get 0.25 eur from me anymore.
Best Regards,
Maria
PD: your solution is not practical because I need the vodafone´s SIM for calls/SMS.
I still feel that Vodafone is cheating. Shame!