I have been plagued with the wait 48 hours to be activated message, like many of you. So I was reading the Apple forums and they said, you need to speak to an activation person at AT&T. So I did and it worked. Do this, step by step:
(1) Call 800-331-0500
(2) Dial 0 and then 0 again
(3) Ask the customer rep nicely to activate you.
(4) Give them your SIM Card # and IMEI. To find this quickly, go to “Settings” on your iPhone, click on “General,” then “About.” The “ICCID” is your SIM card and the one above that, IMEI is the other number they need.
(5) They will ask you to shut down your phone, wait 30 seconds and turn it on.
(6) When the phone turns back on, you should be activated.
LAST item is to make sure your voicemail works. Just call your number, with area code and leave yourself a voice. It will then prompt you a minute later to enter your voicemail password and then your voicemail should work.