If you want to send your voice attachment. You may use the Sound Recorder of your Windows Accessories.
It's a small program that you can use to record your voice with a microphone. But there's a menu that you can use to make the sound special, that is REVERSE on Effects menu.
After recording your voice, you can REVERSE it. Send it to your friend.
If your friend keeps this voice, he/she will have to reverse it in order to hear it.
This effect can be used for fun or to keep important voice message safer than to leave it unreverse (cause most beginners won't know that the voice is reversed voice - most will think that the voice file is broken). Try it!
