Navigate to the Home screen of your iPhone 4. Tap the Phone app, and then tap Voicemail. Tap the Set Up Now button to enter the set up interface.
Enter a four-digit password. Choose a password that you can easily remember. Enter the password again when prompted. Tap the Save button in the upper-right corner of the screen.
Choose between a default or custom greeting. The default greeting may differ depending on your wireless carrier. If you want to make your voicemail more recognizable, choose to set up a custom greeting.
Tap the Custom button. Tap the Record button at the bottom of the screen. Record your custom voicemail message. Tap the Stop button again when you are done recording. Save your message by tapping the Save button.
Play your custom greeting by pressing the Play button. If you are not satisfied with the greeting message, repeat step four until you are satisfied.