function formatUSPhone(sPhone)
{

  var sCleanNumber = stripCharsInBag(sPhone,'(-) ');

  if (isNaN(sCleanNumber))
  {
     // return an empty string -- kill the user's input
     return false;
  }

  if (sCleanNumber.length != 10)
  {
    // return an empty-string -- kill the user's input
    return false;
  }

  return true;

}

function stripCharsInBag (s, bag)

{   var i;
    var returnString = "";

    // Search through string's characters one by one.
    // If character is not in bag, append to returnString.

    for (i = 0; i < s.length; i++)
    {   
        // Check that current character isn't whitespace.
        var c = s.charAt(i);
        if (bag.indexOf(c) == -1) returnString += c;
    }

    return returnString;
}