While travelling in the USA I've noticed a charge from a couple of days ago of £0.01 for using the Internet in zone 1 (1KB) on my UK Virgin Mobile account.
The amount is completely immaterial but I can't see how or why there's any charge when mobile data has been turned off for the last 6 days and the phone has only been used on local WiFi.
If the system can charge 1p for something I haven't done, then what's stopping it charging me more?