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.
From another extension in your system: Dial 500 , enter your extension number, then enter your voicemail password, followed by the # key. Press the * key to enter the Main Menu. Note: If you have no saved voicemail messages, you should enter the Main Menu automatically. You can skip this step. Press 2 to change your greeting.

To save voicemails on most Android phones: Open your Voicemail app. Tap, or tap and hold the message you want to save. In the menu that appears, tap the one that says “save”, “export” or “archive.”
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