New users on Facebook see a security check when sending messages or friend requests. This security check is an image verification, or CAPTCHA. Facebook doesn't turn off the security check until you verify your Facebook account. Using your mobile phone, you can verify your account in a few minutes and not have to do another Facebook security check.
Click on the "Verify Your Account" link in the Security Check box. The link will open the confirmation page.
Enter your country code from the pull-down list. The default setting is for the United States (+1), but other countries are available from the menu. Below the country code, enter your 10-digit mobile phone number and click "Confirm."
Wait for the text message containing your verification code. When you click "Confirm," the page will change to one for entering the verification code. Normal text-messaging charges apply based on the plan you have with your mobile phone service carrier. If you haven't received a text message, click on the "Resend Code" link on the next page to have another text message sent to the number you provided.
Enter the verification number from your text message in the box beside "Code:" and click "Confirm" to verify your account and turn off the security check.
If you aren’t able to receive text messages, you can add a college or university that you have an email address with in your Networks.