// JavaScript Document

 var UNDEFINED;  // do not assign!
 var PHONEMASK = "(###) ###-####";

 function formatPhoneNumber( fieldOrValue )  // example:  formatPhoneNumber(document.formname.txtFieldName);
 {
    if ( fieldOrValue==UNDEFINED ) return(fieldOrValue);
   
    s = (fieldOrValue.value==UNDEFINED) ? (""+fieldOrValue) : fieldOrValue.value;
    if ( s.length==0 ) return(s);  
    s = s.replace(/[^\d]*/gi,"");  // strip out all non-digits before imposing the mask
    s = (s.length>9) ? s.replace(/^([\d]{3})([\d]{3})([\d]{4})([\d]*)$/gi,"($1) $2-$3 x$4").replace(/[ex]$/,"") : PHONEMASK;

    return( (fieldOrValue.value==UNDEFINED) ? fieldOrValue=s : fieldOrValue.value=s );
 }