If you wish to play an office prank, or you just need to send a message to someone without them knowing who sent it, there are websites that will allow you to send anonymous text messages. This way you can send your SMS to whomever you want without them being traced back to you.
Look for a website that offers free anonymous text messaging online. Some good examples are FakeMyText, ChipChick, and SneakSMS (see Resources).
Register for the site that you choose. As of 2010 this is free to do, but you will need to provide your e-mail address, user name, and password. You will also have to confirm your registration via the link sent to you in the email.
Log on to your account and enter the phone number of the person that you are planning to send the anonymous text message to. You can create a fake "From" phone number or you can just leave it blank.
Enter your message. It can be between one and 160 characters long. If it is longer, the message will be divided into two parts.
Go to the verification code that is at the bottom of the page and type it in. This prevents spam from being sent by automated programs. Click the "Send" button and your anonymous text will be sent.