You have to first add your cell phone number to Facebook>Account>Account Setting>Mobile.
You'll receive a confirmation code after that.
Once your phone is added you can text your status to 32665. visit https://www.facebook.com/mobile/?texts=1 to learn how to use the different functions for Facebook Mobile Texts on your mobile phone.
Facebook does not charge you for using Mobile Texts. However, your mobile provider's standard rates for sending and receiving text messages still apply. If you have unlimited text on your plan, you can have unlimited access to this service without any cost.
For more help on this topic http://www.facebook.com/help/?page=821.