This plugins is very cool!
These are things that I think would make it great!
1. Ability for admin to add numbers manually (with/without confirmation)
2. Ability for admin to resend confirmation code from users list.
3. In carriers list, make them selectable. Right now you have to go in a delete each one which takes for ever, without editing code directly.
4. make default style for form, use buttons.
5. In form allow "-" and "." between digits.