Well as promised, I activated my AT&T sim card. I had been told by in store rep and live in chat reps to call the 800# to get it activated and not use Web site for 1st time. After 3 transfers was disconnected. After the next 5 transfers I still least got to the correct department of Prepay Sales. I explained I had the N7 and an installed sim card and wanted to purchase a month of data. Well low and behold hevhss no idea how to do this. "Well on the iPad thus us here and you go here...." Finally, the genius says you should do it through the website but I will stay on the line to make sure it works when done.
I filled out all the information as required and got a confirmation that I purchased 3GB to be used from 1/7/2013 10:48pm to 2/6/2013 10:47pm.
Before I started calling I had shut off my wifi and Bluetooth and turned mobile data on and N7 powered off.
Power on says AT&T on bottom of lock screen and a data lines like a mobile phone with 5 bars. I tried websites on Chrome over and over. Once purple.com did appear. Couldn't get Google.com or att.com, Nada.
Rep tried to resend signal, I turned N7 on and off a few times. Finally, I went to settings>more>mobile and made sure mobile data was on and also 2G was unchecked. I went to check Access Point bd made sure ATT Broadband was checked. Next I went to APN and used the 3 dots (menu) and chose default. After backing out I was able to pull up a couple Web sites.
It was slow and dragging slower than a slug so I turned it off. About 20 minutes later I turned it in and switched off wifi and put on mobile data. No problems at all now. I pulled up most websites on Chrome and Dolphin. I even tried playing Words with Friends with no problems.
Sorry for the very detailed information.
Try finding APN and reset default. Also, verify mobile data is checked on and wifi off.
Sent from my VZW Samsung Galaxy S 3.