To lay the cables required a huge amount of capital, to make that feasible its required financial engineering. That translates to high operating expenses.
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.