Fix validation of phone number on html form, simple project

Hi I'm looking for soneone with good experience in javascript, html and wordpress. The task is that I have a wordpress site with a form, the problem is tat people signup on that page with wrongly data. So the leads are not valid. I'm looking for someone to add validation to the form so it checks that people enter phone number in correct US format. If wrong give a good error message to the user so he knows what is wrong. Have example script from another site that can help you on the way too.... If you have tips on how to increase the conversion that would be a bonus :) (could have done this myself as I'm a programmer, but post it here because I have little time for such programming when I'm home) I can PM you link to the site if you want that before you bid