I am trying to create a an function that formats US phone numbers -- hopefully without looping through each digit.

When 10 digits are passed in all is fine. How ever when more than 10 digits are passed in I want the String.Format method to append the extension digits on the right. For example:

When 14 digits passed in the result should be:(444)555-2222 x8888 When 12 digits passed in the result should be:(444)555-2222 x88 etc. However what I get with my current attempt is: Passing in 12 digits returns this string '() -949 x555444433'

here is what I have so far.

public static string _FormatPhone(object phonevalue)
{
    Int64 phoneDigits;

    if (Int64.TryParse(phonevalue.ToString(), out phoneDigits))
    {
        string cleanPhoneDigits = phoneDigits.ToString();
        int digitCount = cleanPhoneDigits.Length;

        if (digitCount == 10)
            return String.Format("{0:(###) ###-####}", phoneDigits);
        else if (digitCount > 10)
            return String.Format("{0:(###) ###-#### x#########}", phoneDigits);
        else
            return cleanPhoneDigits;
    }

    return "Format Err#";
}

Thanks in advance.