If you have unlimited texting, its cheaper than calling. Its also good if you just want to send a quick message like where to meet someone, let somone know if u will be late, ect. I never texted til i met my present GF. Her and her friends use texting too much. i personally dont want to text a whole conversation. Its a pain. I feel that if I want to have a conversation, I will just call. The worst part about texting, is the people who do it while driving. most people have a hard enough time focussing as it is, let alone with a phone in their hand or some other gadget.
I use facebook, but not all that often. My GF is on mine more than I am. This whole twitter thing, Im not sold on. Maybe its just the dumb name... I dont know, but one thing i do know is i dont need it. Between email, phone, RCU and facebook, I already have too much going on at once.