Do you find yourself putting pen to paper, staring blankly at the wall, searching for just what to say? Well, know that it happens to the best of us. To help you out, we’ve included some voicemail greeting samples for you to look at. Both the 10 formal and 10 informal samples should give you the prompting you need to start crafting your own voicemail script.
On the iPhone, go into voicemail and tap "Greeting". Record a few seconds of something and tap stop. Before you tap save, use iFuntastic or SFTP to navigate to /var/root/Library/Voicemail on your iPhone. You'll see a file called "Greeting. amr". This is the audio you just recorded. Delete that file and replace it with your custom message which should then be renamed to "Greeting.amr". Tap "Play" on the iPhone to verify your message works. If it plays, tap "Save" and your custom message will be uploaded to AT&T's servers.

You could use this website as a free voice over generator for narrating your videos in cases where don't want to use your real voice. You can also adjust the pitch of the voice to make it sound younger/older, and you can even adjust the rate/speed of the generated speech, so you can create a fast-talking high-pitched chipmunk voice if you want to.
.Oh - if anyone is still curious: I recorded the greeting via the phones custom greeting function, then called to listen to it from another phone, then turned off the phone and called again. Same message. I had wondered if just maybe the phone played the message when on, and the carrier played the message when the phone was unreachable.