[resources used within network to route, store and forward message, payment made to peering network to which the target phone is connected to] I spent two year

[resources used within network to route, store and forward message, payment made to peering network to which the target phone is connected to] I spent two years working on carrier software for this section of the SMS transmission procedure and there are plenty of things here which cost the carriers money. SMS is definitely not free to the carrier. Also, from my understanding, they don't actually piggy-back on the control messages, at least not after they have entered the wired part of the system (I never worked in the over-the-air part of the system, so have no knowledge of what happens there). That is, even if the control messages were sent constantly, SMS messages don't get a free ride, but rather they share the bandwidth with the control messages, since those messages do not require near as much bandwidth as the voice channels do. As an aside, one carrier we installed our system in could only handle a thousand or two messages per second tops, after that, messages were dropped (well, TCAP transactions meant they were re-transmitted later), so there isn't some magical unlimited bandwidth available to SMS messages.