that if you're really worried you can always opt for BT's premium rate and international number call barring service for £1.50 a month. Some helplines are using the 090 prefix however, and if you want to use these numbers you'll need to ask BT for the flexible call barring facility that you can turn on and off - this costs £1.75 a month. Call BT on 150 to set it up.
It's sort of on the same subject. It occurred to me that perhaps it would be technically possible for BT to warn users whenever an 090 number was dialled from a phone or modem, in the same way that the plummy voice tells you that the number you have dialled has not been recognised. If you were using the phone and intended to dial the 090 number then pressing, say, the hash or star key would allow you to continue, and if you were using a modem a message could be put up on the screen and over-ridden by another key stroke if you wanted to proceed. If this kind of technology has been available but not introduced by BT it casts another light on their insistence that they only get a small return from 090 numbers. Can you shed any light on this?