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.
Informal voicemail greetings are those that don’t adhere to the rules of professional and business voicemail greetings. Here, you are free to just leave a simple greeting, or use it to show your more witty side. This style of greetings can be used for both home and business if you like, depending on the type of caller you expect. For instance, a novelty shop could probably create a rather informal message, using sound effects that represent the type of items they sell.

Thank you for calling (company or person) we are not available or are on the other line with another customer, please hold and a representative will be with you shortly.
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