Sometimes they are enabled without your permission. My mom's phone number auto-magically gets subscribed for 'premium SMSs'. She doesn't understand how to send SMS's and cant use the phone interface apart from dialing a few numbers. Yet she often complains of money getting deducted from her pre paid account.
Called the customer care numerous times and every time all we get is - 'We are sorry sir, may there was an error in our system'.
Needless to say these mobile company thieves make millions from these 'errors in the system'.