window.onload = initPhoneFields;

function initPhoneFields()
{
    if (document.forms.length > 0)
        {
            for (i=0;i<document.forms[0].length;i++)
                {
    	            if (document.forms[0][i].className)
                        {
                            if (document.forms[0][i].className == "form_phone")
                            {
                                document.forms[0][i].onchange = formatPhoneNumber;
                            }
                        }
                }
         }
}


function formatPhoneNumber()
{
    field = event.srcElement;
             
    if (isNaN(field.value))
    {
              
    }
    else
    {
        if (field.value.length == 10)
            {
	            newVal = "(" + field.value.substr(0,3) + ")" + field.value.substr(3,3) + "-" + field.value.substr(6,4);
                    field.value = newVal;
            }
    }                
}