What app do you use on your iPhone 4S to send an unknown message?

To send an unknown message on an iphone 4S, you can use the built-in Messages app, which allows you to send SMS or iMessages. Alternatively, you could use third-party apps like WhatsApp or Signal, which offer encrypted messaging features. If you want to maintain anonymity, consider using apps like TextNow or google Voice, which allow you to send messages without revealing your personal phone number.