format us phone number

function formatPhoneNumber($strPhone)
{
$strPhone = ereg_replace("[^0-9]",'', $strPhone);
if (strlen($strPhone) != 10)
{
return $strPhone;
}

$strArea = substr($strPhone, 0, 3);
$strPrefix = substr($strPhone, 3, 3);
$strNumber = substr($strPhone, 6, 4);

$strPhone = "(".$strArea.") ".$strPrefix."-".$strNumber;

return ($strPhone);
}