Here’s how:

Click the Messenger menu and select "Sign in to Mobile Device."

Select a country and service provider from the pull-down menus and click the Continue.

Choose the device type and create a name for your phone. Click the "Next" button.

Enter phone number and click the "Next" button.

A confirmation code will be sent to your device. Enter the code and click the "Next" button.

Your mobile device is now registered.

Note: If you don’t receive the confirmation code within 10 minutes, repeat the registration process. If you still don’t receive the confirmation code, try sending an email message to your mobile device. If you STILL don’t receive either message, contact your mobile service provider to find out if your mobile device can receive text messages.