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.
To record custom greetings simply click Record custom greeting, then hit Tap to record and start recording.

Extension users can dial voicemail feature code (default *2) on their phones to access their voicemails. To enhance the extension security, you can change the voicemail PIN on PBX web interface.
To commemorate the tenth anniversary of the iPhone, Apple marketing chief Phil Schiller sat down with tech journalist Steven Levy for a wide-ranging interview about the smartphone's past, present, and future. The report first reflects upon the iPhone's lack of support for third-party apps in its first year. The argument inside Apple was split between whether the iPhone should be a closed...