Heath Gibson responds to my observation that, per bit transmitted, SMS is about 100 000 times as expensive as Internet or voice telephony. As he says, cost per KB isn’t everything. If you don’t have easy access to email, don’t have or want to use a home phone, only want to transmit a little bit of info and don’t need a reply (which doubles the cost relative to a voice call), SMS looks pretty good. But how can a niche like this account for 75 million messages a month?

The Telstra publicity Heath links to reveals the answer. Mum and Dad are paying the bill