It is better then talking on the phone. It is good for multi-tasking. Also, when you are on the phone with a girl, she can tell that you really don't give a shit about what she is saying, with texting, she doesn't know you don't give a shit.
Well if a girl I was fucking called me up and I said "I really could give a shit about anything you have to say so I am going to hang up the phone now," then she more than likely would not want sex as bad.