The price of what unlimited text messages should cost aside, the ala carte pricing of text messages (at least for US cell carriers) is definitely price gouging. It cost (at least at one point) ~25c to receive a text message. And I have received spam text messages. This creates a perverse incentive to the carrier to do nothing to block spammers on their SMS network.

Also, my wife has a pay-as-you-go plan and each text that she sends or receives counts as a minute of talk time. I have a hard time believing that setting up circuit from one end of the text to the other takes the same amount of resources as a minute of talk time. Shouldn't a minute of talk time also take up a circuit? Wouldn't a text occupy that circuit for a fraction of a minute?