ankytt on "Mobile Number Field in Sign up Form + SMS api"

Hello Guys,

I am trying to create a sign-up form with mobile number. I was able to add the text field using this tutorial:
http://codex.wordpress.org/Customizing_the_Registration_Form

Now, I want to customize the field so that it accepts only 10 digit number. Users should be able to modify this mobile number later on their profile page. Also, I am using a SMS API. So, i want to send a welcome text to this mobile number when user successfully register and when he makes a request to reset the password.

How should i do this? My SMS api is a simple HTTP api.

Thanks,
Ankit A.