For me, two words describe SMS messaging. Incredible rort. 20+ cents (AUS) to send < 160 bytes to another handset? I think not. I would estimate cost to the network would be in fractions of cents, if that.

Don't forget that your handset is already constantly sending and receiving data with the network, just because it's turned on. Your phone may be showing which cell you are currently residing in. How do you think it knows this information?

Also don't forget that the cellular network was most likely provisioned and costed for without factoring in text messaging. However, text messaging cost to the network is surely negligible compared to the cost of carrying a call. SMS messaging is very likely to be close to 100% profit to your telco.

Wish it wasn't so damned addictive.

More than that, I wish I was CEO of one of those Telco's.