It's not just that — SMS actually get delivered as part of the unused signalling capacity as far as the airwaves are concerned, hence the 160 7bit limitation, t

It's not just that — SMS actually get delivered as part of the unused signalling capacity as far as the airwaves are concerned, hence the 160 7bit limitation, to fit into the existing protocols. E.g., as far as the the costs go, I'd argue that airwaves would be most expensive in something like SMS, as it's a limited and finite resource that has to be shared by everyone within a given geographic area, yet they're basically used for free here due to the signalling already being mandatory even without SMS, so, any charge for SMS is basically pure profit by selling a resource that has to exists just for the signalling alone. If someone knows more about how is managed between ME and the tower, please correct me if I'm wrong. There's also the cost to run SMSC (Short Message service center), but that part would be done in the cloud, and cloud is a pretty commodity resource nowadays, where these sorts of costs per message can hardly be justified, so, basically, it'll probably be the billing itself that contributes most of the cost to the cost of SMS. P.S. Fun fact: I took a course at UWaterloo (in Canada) about the maths behind the computer networks, and during the time of the course, my professor has testified as a witness for US Government about the rising costs of SMS — https://www.c-span.org/person/?srinivasankeshav https://www.c-span.org/person/?srinivasankeshav.