I see a couple of reasons why texting would not be considered kesiva. Some poskim (perhaps not most, but I have heard of it) do not consider disconnected dots to be a ksav (the context in which I heard this was opening a bottle cap with the date on it). Also, unlike all of the examples found in poskim of ksav she’eino miskayeim, there are no real letters, just an electronic simulation. Saying, however, that there is no meisah k’sivah is wrong; if we were to consider the ksav to be a ksav, pushing the buttons would be a meisah k’sivah.
However, all contemporary poskim accept the view that any use of electricity is assur either mid’rabbonan or mid’oraisa, so using a phone to text would definitely be assur, and any statements to the contrary are pure rationalization.
The reason people text, IMO, is because it is addictive behavior. Although, as aries pointed out, many smokers don’t smoke on Shabbos, unfortunately, some do.