Currently the issue of unexpected charges is something that is generally very poorly handled by the mobile operators - I have first hand experience of children running up substantial bills because there were no warnings or alerts about expenditure. Where are the hooks that pick up unusual spending patterns? It's no good expecting customers to dig around your website looking for unbilled usage data - you need to push the information out to customers so that they remain in control. When a customer starts using data when roaming, warn them by SMS of the consequences, when usage hits a 'dangerous level' temporarily suspend usage until they confirm it's okay. When a customer approaches their call or text bundle limit, warn them they will start incurring extra charges. Help customers to help themselves.
And don't do what one of the big UK mobile operators does, not make unbilled data available to customers until after the customer has received the first bill - by then it might be too late!
