You can easily send a text message from your computer using your favorite email account. The secret is knowing how to address the message. I have compiled a little list of the most common cell phone carriers and how you need to format the address to insure that your text message reaches your intended recipient.
Sprint - email@example.com
T-Mobile - firstname.lastname@example.org
Verizon - email@example.com
Now put down that phone and get text messaging!