I agree, I don't understand why we all don't just call each other and tell eachother our comments instead of leaving these text messages on this website.
But seriously, text messaging is much less invasive and demanding of both parties for communication. If you want to communicate something non-vital that doesn't need an immediate response, which is more convenient? Initiating the call, waiting to see if they pick up (also forcing them to decide if they want to stop what they're doing at that exact moment) and then having the quick conversation and then saying your goodbyes, or sending the message and letting them decide when to stop to read the message and whether or not they want to / need to respond / when they want to respond. Then you also have record of everything that was sent and received. Also, what's easier, trying to read numbers or email addresses etc over a phone line or just sending it in a text message? (Did he just tell me to buy elephant shoes or did he say "I love you"?)