I too would like to see some kind of block. I have had the same mobile number for over ten years. In all that time I have NEVER requested any kind of subsription via sms and yet in the last year I seem to get more and more of these messages that I have no interest in. It may only be about £3 extra a month, but for goodness sake, I went onto a cheaper tariff to save that much money a month!
It's all very well texting STOP but then that's another £1.50 I had no interest in spending so my bill gets hiked up by nearly £5! We already know our details are being passed on to third parties whether we like it or not. Why isn't there a service to protect us from other companies' dishonesty?