Ok, then clearly explain how you think they work. I for one already know. Oh you wish to know?
Well, Text messages piggyback on top of the same signal used to determine how many bars your mobile should display. That is why SMS/Texts are limited to 160 characters (well 128 when SMS was developed, but the scientist behind SMS thought 160 was perfect, in the end he got it). In other words, SMS/Texts piggy back on your phone power signal and end up costing the carrier next to nothing.
Hence you see all those posts saying texts are still 99.9% profit, because in reality they are.
Now does that help your small mind? Does it?