That's only in some countries (eg: US). In other countries, SMS is way cheaper for example, for the cost of a dollar or so, you can get a plan that allows you "unlimited messaging" or some obscene number of messages per day (more than you can reasonably type). For example, I know this was the case in India as recently as a couple of years ago -- and then they capped it to try and stop telemarketing spam.
So there are definitely places where SMS is cheaper than data access. In the US it's inverted purely due to the business model choice of the carriers.
vidarh
These plans are only "unlimited" because nobody is using them as high bandwidth data channels.
Try to push high volumes through it, and expect to see SMS's delayed - SMS can be delayed for hours at the whim of the operator - or simply dropped, at the whim of the operator. Or simply rate limited.
So there are definitely places where SMS is cheaper than data access. In the US it's inverted purely due to the business model choice of the carriers.