Mobile number registration in facebook
First log-in to your Facebook account from PC of any browser. Then go to the Account (Right corner). Then go to the Account settings. A page will appear. In left side corner, there will be seven options. They are: General, Security, Notifications, Applications, Mobile, Payments, Facebook Ads.
Click on the Mobile option.  A page will appear. There is a box colored Green named  Add a phone.  Click on the box, a window will appear. Follow the steps and your mobile number will be registered.
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Mobile number registration in facebook
Hi,
If you don’t have any facebook account then, first fill the form by entering your details >> click Sign Up button>> go to your email>>click Face book activation link>>you can upload your profile Image and setup your account details.If you want to add your phone number, you can add it in this step.
If you already have a facebook account, go to the Account setting>>you can change your details >>click Mobile link left side of window>>click Add a Phone button>>select country and service provider of your mobile>>click add your phone number link>>enter the phone number>>you can receive a verification code to your mobile>>enter verification code and continue