Hey, I was having a similar problem with mobile.o2.co.uk charges appearing for no apparent reason. O2 customer services were useless and wern't even willing to tell me WHY I was getting charged
I phoned trading standards aand they told me that under the Supply of Goods and Services Act, O2 HAD to supply me with a solution to these anonymous charges.
Surprisingly, after I told O2 this, they were all over a solution and they have now shut down the mobile.o2.co.uk APN on my account. This is no way has affected my usual internet use but anything that tries to charge can't connect (including using as a modem)
I understand that though this might not be a solution for those of you who want to use your phone as a modem, but if you simply want the charges to stop like I did, this works great.
Feel free to quote that bit of law, it puts their tails between their legs! I hope this helps.
LordJoeHo