You can use TextPort.com. www.textport.com. They support free texting and picture texting to all US mobile providers. You can send anonymous texts from this site.
How Do I Send An Anonymous Text Message Without My Phone Number Showing?
Simply go to your phone account. For example. (go to verizon and enter your number and it will take you to your account. From there click where it says send text and it will let you send it anonymous)
Go to this site and text from there, be sure to select the right carrier of the phone you are texting to www.txt2day.com