Re: Formatting telephone number in ValidationTextBox.
You’ll need a custom on onBlur / onChange event to do it. With
the regEx the textbox will think it’s not correct when first enter causing it
blink yellow before you custom handler reformats the number.
I was looking for the same type of solution, and after not finding one I experimented until I created what works for me. It extends ValidationTextBox, overrides onChange, and uses the "placeHolder" attribute to define the desired format that it then enforces. Check it out at jsfiddle: http://jsfiddle.net/gregorco/m7fJ9/11/
At the moment it has a less than perfect way to consider a phone extension "x###" as optional - so if you see a better one, please improve it. Thanks.