That's the excuse that is used by farmers in Britain.
We subsidise growing sugar beet in Germany rather than importing cane sugar because in WWII German U-boats cut off the imports.
When free evening/weekend calls were first introduced there were stories of people using their cell phones as baby monitors - the phone co had to introduce a one hour maximum call length.
The over the air part of SMS can be zero cost. The SMS message is in a spare 128byte segment of a standard phone-base status message (it can send a new packet specificaly to transmit the SMS but it doesn't have to if you don't mind a few mins latency). If the receiver is on the same base station -like kids texting each other across the classroom it doesn't use any of the phone companies network bandwidth.
It takes more bandwidth to send a message back to HQ to
bill for the text message than it does to transmit the SMS.