Ironic timing...
I just got a text from someone getting back to me about an appointment I had requested -- which I also made through text instead of calling.
Another reason I choose writing for almost all my communication is so that I have irrefutable proof that an appointment was made, a service was promised, a change was agreed upon, etc.
It's a sad fact of modern life, but you just can't trust anyone's spoken word these days. I think we've all run into times when a doctor's office, insurance agency, or some other business has tried to say they said this or that, or, "No, your appointment was for the day before and you missed it, so now we're charging you" (such as doctors' offices will do,) etc. Or, "No, we never promised such-and-such..." but the representative had told you differently on the phone.
So as a means of trying to watch my back whenever I can, I always feel most secure when I can get any term of agreement in the form of a timestamped message in writing that can be produced in the case of any dispute.