function stringFilter (input,fchars) {
	s = input;
	filteredValues = fchars;
     	var i;
	var returnString = "";
	for (i = 0; i < s.length; i++) {  		
                     var c = s.charAt(i);
		if (filteredValues.indexOf(c) == -1) {
			returnString += c;
		}
	}
	return returnString;
}
function formatUsPhone(field){
	
	pn = field.value;
	slen = pn.length;
	pn = stringFilter(pn,"()- abcdeffghijklmnopqrstuvwxyzABCDEFFGHIJKLMNOPQRSTUVWXYZ");
	var newp = "";
	for (i=0; i<slen; i++){
	  	val = pn.charAt(i);
		if (i == 0){
			newp = "(";
		}
		if (i == 3){
			newp += ") ";
		}
		if (i == 6){
			newp += "-";
		}
		if (i == 10){
			newp += " - ext ";
			//break;
		}
		newp += val;
	}
	field.value = newp;
}