Text messaging is one of the most idiotic things ever invented. You already have the phone in your hand why not just call them and say what you want for free?
I'm just waiting for all the new medical conditions and lawsuits that follow from years of text messaging.
I got into a debate with someone on this a few years ago, when text messaging was just starting to get popular 
Things you can do with a text message a lot easier than a phone call
A) Confirm an appointment (say, lunch) with multiple people.
Case and point: It's a lot easier to text "Hey, are we still on for lunch?" to 8 people, than to call each one.
B) Break up with your girlfriend/boyfriend
Case and point: "I'm sorry, this just isn't working out..."... it's that easy 
C) Send an invitation to people
Case and point:Hey ya'll, we're going to see Incredible Hulk tonight @ 8:00PM at AMC16. Let me know if you want to come!
D) It's just quicker most of the time...
Case and point: Even though people will argue "why not just pick up the phone", I can send a text message to someone saying "Hey, are you still going tonight?" a LOT quicker than calling them 
I disagree; Actual speech is generally better.
A) Redundant with C. Just a means of communicating with mulitple people. In this case, you're not actually talking with them, and is entirely unsimilar to any kinds of conventional conversation. But you are correct, it's more effective.

B) Fine I guess, albiet potentially problematic in the future - moreso than would be if actual conversation had taken place.
C) See A.
D) Invalid argument. Some people are much quicker actually talking, rather than text messaging. Coincedentally, those are the people who don't text. Anyway, you're essentially just restating your point here, and it's too debateable. Course, that doesn't necisserily mean that talking is better.

You see, most normal people (that I know, at least) don't have cell phones purely to confirm appointments with peoples, or invite peoples, or break up with a person. Most people that I know have phones to actually communicate with people, which is largely ineffective on a 9-button phone with a 26 letter alphabet (not to mention capitols and punctuation). The situations you listed are somewhat numerous in type, but they make up such a small percentage of actual phone usage, that compared to the part of usage that it
is useful to talk, is almost ridiculous. If people want to text people, get a pocket computer with wi-fi and AIM, and for that matter a full keyboard.
