Q: how to activate cellular data in ipad air?

Hello there, priya25.

The following Knowledge Base article offers up some great information and steps for troubleshooting cellular data connections:

iPad (Wi-Fi + Cellular Models): Troubleshooting a cellular data connection

http://support.apple.com/kb/TS4249

Follow the steps below, testing after each step.

1. Check for a carrier settings update:
   1. Make sure your device is connected to the Internet.
   2. Tap Settings > General > About.
   3. If an update is available, you'll be asked if you want to install it. Tap Update.
2. Update your iPad with the latest version of iOS.
3. Toggle the Cellular Data setting off and on under Settings > Cellular Data.
4. Restart your iPad.
5. Tap Settings > General > About. Locate the Carrier entry and make sure that your carrier is correct.
6. If your SIM card has SIM PIN enabled, try turning it off: Tap Settings > Cellular Data > SIM PIN.
7. Make sure you're in an area of good coverage. If the cellular data connection works in another area, contact your carrier to report the original affected area.
8. Reset network settings: Tap Settings > General > Reset > Reset Network Settings.
9. Restore the iPad as new.

If none of the above steps resolves the issue, make an appointment at an Apple Retail Store, contact your carrier, or contact AppleCare to troubleshoot further.

Thanks for reaching out to Apple Support Communities.

Cheers,

Pedro.