User reg process with SMS mobile confirmation also. How?

Hi

I have a scenario where I want the registration process also involve that users can only have an obligatory registration with their mobile number attached to profile in the second step after they have confirmed their email account too..

Similar like Facebook doing for second step: "When you add your number here, Facebook can use it to help you log in, protect our community, accurately calculate how many people use our services, and help you access Facebook and optional programs. The number is not used to suggest friends, display advertisements or the like. Only you can see the number in your profile. If this number is provided in another of the Facebook companies' products, it may be used for other purposes, for example to suggest friends and display advertisements."

How can you add this step to prevent spam fake users etc also for EasySocial registration process? So you lock this mobile number so it cant be used anymore for anyone else check up too...

ie one profile user = one mobile no per user

Pls come back asap how to do this..