> SMS was originally piggybacking off unused bytes in packets already being sent to the tower

for GSM? not really, Yes SMS was sent at a lower priority than voice, so if there is a lot of voice traffic, SMSs wouldn't be delivered as quickly.

But, to my original point, do you think the towers were free?

Thats the point, it took a shittone of captial to make the network.

Did the mobile networks make a lot of cash? also yes. But they also took on huge amounts of debt and went bust.