How to Activate Visual Voicemail on an Unlocked AT&T iPhoneby Nicholas Smith
If you have unlocked your iPhone and can no longer access Visual Voicemail, know that this is a common problem. Visual Voicemail combines traditional cell phone voicemail features with a graphical interface. Fortunately, enabling Visual Voicemail on these devices may be done in a few simple steps.
Open the phone application by clicking "Phone" and tap the "Keypad" function.
Obtain the voicemail number by entering " * # 6 1 # " (without quotes) and pressing call. The voicemail number will appear on the screen.
Enter the following number: "*5005*86*phonenumber#". The "phonenumber" phrase is the number retreived in Step 2.
Press "Call" to activate Visual Voicemail.