Formatted Phone Number String

/**
 * @updated: 2014-07-29
 * @source: http://stackoverflow.com/questions/6052966/phone-number-formatting
 */
-(NSString*)phoneNumberString
{
    static NSCharacterSet* set = nil;
    TL_DISPATCH_ONCE(^{
        set = [[NSCharacterSet decimalDigitCharacterSet] invertedSet];
    });
    
    NSString* phoneString = [[self componentsSeparatedByCharactersInSet:set] componentsJoinedByString:@""];
    
    switch (phoneString.length) {
        
        case 4:
        case 5:
        case 6:
            return [NSString stringWithFormat:
                    @"(%@) %@",
                    [phoneString substringToIndex:3],
                    [phoneString substringWithRange:NSMakeRange(3, phoneString.length-3)]];
        
        case 7:
        case 8:
        case 9:
        case 10:
            return [NSString stringWithFormat:
                    @"(%@) %@-%@",
                    [phoneString substringToIndex:3],
                    [phoneString substringWithRange:NSMakeRange(3, 3)],
                    [phoneString substringFromIndex:6]];
        
        case 11:
            return [NSString stringWithFormat:
                    @"%@ (%@) %@-%@",
                    [phoneString substringToIndex:1],
                    [phoneString substringWithRange:NSMakeRange(1, 3)],
                    [phoneString substringWithRange:NSMakeRange(4, 3)],
                    [phoneString substringFromIndex:7]];
        
        case 12:
            return [NSString stringWithFormat:
                    @"+%@ (%@) %@-%@",
                    [phoneString substringToIndex:2],
                    [phoneString substringWithRange:NSMakeRange(2, 3)],
                    [phoneString substringWithRange:NSMakeRange(5, 3)],
                    [phoneString substringFromIndex:8]];
        
        default: return phoneString;
    }
}

// UITextField Usage
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if (textField == self.phoneNumberTextField) {
        NSString *text = [textField.text stringByReplacingCharactersInRange:range withString:string];
        textField.text = text.phoneNumberString; // implemented as a category on NSString
        return NO;
    }
    return YES;
}