How does texting work with Facebook messages?
Once you activate text messaging for Facebook, the texts you exchange with friends are incorporated into your conversations along with your message and chat history. This allows you and your friends to message each other even when you’re not at your computers.
Getting and responding to messages from your phone
Once you turn on text messaging feature for Facebook, friends can check the “Send to Phone” option when they send you messages. If a friend checks this box, you will receive a text that contains the message. Simply reply to the text from your phone, and your friend will receive your reply as a Facebook message. It will also be logged in the ongoing conversation with your friend, which you can view from your Messages home page.
Sending messages from your phone
To send a new message to a friend via a mobile text, just text the following to 32665 (FBOOK):
msg john smith what’s up?
This would send the message “what’s up?” to your friend John Smith.
(This short code may not work in India currently. Wait for more updates.)
Controlling text notifications
You can control which text notifications you receive on the Notifications tab of your Account Settings page. Read More on Facebook Text Messages – Activation, Control and Use of SMS.