I would say go to meebo.com for IM. Its the best IM out their for the touch/iphone in my opinion. But if you are a=talking about actual "texting" no you can't do that as its over the cellular network and the touch is not a cell phone.
I know you can send text messages to people who use alltel and sprint as an email. I currently have alltel and you have an email address like ##########@alltel.messaging.com.