Cellular data button

Settings ...
"Cellular Data" should be the 5th item from top on the left.

Nothing that needs to be installed

Strange .. under Settings - left column I've got the following items (from top):

Airplane Mode
Wi-FI
Carrier
Notifications
Cellular Data
Brightness & Wallpaper
Picture Frame
....

Is it possible to scroll/move up-down that left column "Settings" on your iPad?
2nd guess - if your iPad is Wifi only - there won't be a "Cellular Data" item

Have you got a WiFi only iPad?

Do you have a black bit on the back of your iPad that is on the opposing end from the home button?

(Sorry if this is a stupid question but it sounds like you have a wifi only iPad, to login to a cellular data account you would need a 3G iPad)

I don't know. My only suggestion is contact AT&T and talk to them. As far as I know, you cannot access your cellular data account to use it on the ipad without having a 3G iPad. If you recently purchased it I believe you can return it to an apple store and then purchase a 3G+Wifi iPad if that is what you are looking for.

Assuming that you've got a wireless access point in range:
You can connect through "WiFi"
Tap onto it - switch it "ON" then select a WiFI net

I have a 64GB 3G-WiFi (Model No. MC497LL) with the same symptoms. Having spoken to the Apple Expert, it was confirmed that its a faulty unit and will be replaced.

Possibly a stupid question but do you have a 3G + WiFi iPad? If you have a WiFi only iPad, you won't see the Cellular data button.