There are a number of ways of doing this. What kind of text message content are you looking to send? You can simply set up a script to send them via an email client. an example to send a text message to a Verizon cell phone the address is the phone number in this format.
Each carrier has its specific domain to be used like these
Metro PCS: @metropcs.sms.us
U.S. Cellular: @email.uscc.net
Virgin Mobile: @vtext.com