In Russia they used to do that; later on the telcos were forced to require an explicit confirmation: a code would be sent to subscriber which they then has to willingly submit in order to subscribe.

And now half of the malware and shady websites would ask for your phone number and then trick you into telling them the confirmation code.

I think that such services should be illegal in the first place. That's the only way to protect subscribers. And they need to be protected: imagine it can be your granny who will end up paying tens of dollars monthly for nothing (I've got the impression they don't even send the SMSes you "subscribed" to, just charge the money)

I can't imagine a SMS subscription worth ten bucks monthly. Every one of them is a fraud.