How to activate Cellular service for iPad Air

Almost. You need a separate connection, which will have an identifying number that probably looks like a phone number (depending on your telecommunications carrier) but cannot be used for phone calls or SMS/MMS messaging.

Assuming the iPad Air you bought included the cellular hardware rather than being the wifi-only model, you may be able to activate cellular service from within the Cellular panel of the Settings app. Again, this may depend on your carrier.

If your Settings app doesn't have a Cellular panel, you may have bought a wifi-only iPad.

iPads don’t have telephone numbers and can’t make phone calls.