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.
.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.

Once you finish your voicemail message, you can end on a note of gratitude and express thanks or that you realize the recipient of the message us busy, so you’d appreciate a return call. Whichever way you choose, make certain that the tone of your message is upbeat. A business voicemail greeting sees each call as their chance to engage with their clients or vendors. Hello, you’ve reached the office of Lydecker and Lydecker. We are currently unavailable to answer your call. However, your call is important to us, so please leave your name, phone number or email address, and a brief message and we’ll get back to you as soon as possible. Thank you for your interest in Lydecker and Lydecker Law Offices. Professional tone Provide the caller with specific information Request the caller to leave specific information Extend gratitude for their call Professional Voicemail Greetings
If you have an iPhone and would like to change your voicemail greeting, here’s how to change voicemail greeting on iPhone step by step!