All cell services still require a tower. But text messaging is done on a control channel which doesn’t require a voice channel to be vacant so you can get it out if you’ve any connection to any tower across even greater ranges. Whereas you may be too far out to carry on a voice conversation or grab a voice channel the tower will still relay a text.
Hmmmmm ..?? My son never explained it to me that way; but it’s good to know .. thanks.