Simply format number to US phone format using JavaScript, look at example on http://jsbin.com/etede5/5

US_phone_formatter.js

var number = "1234567890";
var formatted_number = "";
var number_of_digits = number.length-1;
var bracket = false;

for(var i=number_of_digits; i>=0; i--) {
  var digit = number[i];
  var position = number_of_digits-i;
  
  switch(position) {
    case 4:
      formatted_number = digit+'-'+formatted_number;
      break;
    case 7:
      formatted_number = digit+') '+formatted_number;
      bracket = true;
      break;
    default:
      formatted_number = digit+formatted_number;
  }
  
  if ( bracket && position == number_of_digits )
    formatted_number = '('+formatted_number;
  
}

alert(formatted_number);