Select the Voicemail tab. Below "When callers reach my voicemail, play my," select one of the following types of voicemail greetings: System Greeting - Plays a system generated message that utilizes your recorded name and is the default setting for all new users. Personal Greeting - Plays a custom message that you record using a phone.
3. Setting Up an AT&T Visual Voicemail: Open your iPhone's Phone app. It's the white phone icon on a green background on the Home screen. Tap "Voicemail". It's in the bottom right corner of the screen.

Select "custom" and tap on "Record" in the bottom-right corner of the screen. Tap on "Stop" when you finish recording. Select "Play" to play back the message. If you are satisfied with your new message, select "Save" in the upper-right corner.
If you’ve already created a custom voicemail on your iPhone, you can tap Play to see how your voicemail sounds. If you’re interested in creating a new message, tap the Custom button. From here, you can start recording your message by tapping Record and tapping Stop whenever you’re finished. Once you’re finished recording, tap on Play to make sure the message comes across as you’d like and hit Save (in the upper right) to save it as your voicemail.