Call API using custom field

Hello There,

First of all, thanks for creating this beautiful plugin. It has saved me a lot of work. Now, i am trying to modify the sign up form via this plugin. I needed a mobile number field on my sign up form so i created a custom field via this plugin. I have kept it as textbox field and given it database key as rpr_mobile_number. Because it is a mobile number, what i need is some kind of validation so that user can’t enter more than 10 numbers(not text). How do i do this?

Also, I do have SMS API with me so i want to send a welcome text on user’s mobile number. Is it possible?

Thanks,
Ankit A.

https://www.ads-software.com/plugins/register-plus-redux/