First off I am curious as to what your saying an SMS is exactly? Are you talking about instant messaging?

And one might assume that logic would dictate that what is and isnt considered infidelity should be defined by those actually in a relationship between each other.

Where as logic doesnt nessesarally preclude, as is sugested by the spurious corelation in the quoted passage above: that interaction through long distance forms of media being more prevelant must also mean that people are being any more or less true to one another in their relationships.