Airtime

Jack Bauer (Kiefer Sutherland) using his mobile phone on 24
Jack Bauer (Kiefer Sutherland) using his mobile phone on 24
Definition: 

Airtime is the actual time spent talking on a mobile phone. This is the time measured by mobile phone operators (or carriers) when they calculate your bill.

It is typically measured in minutes for voice calls.

Mobile phone makers differentiate a handset's battery life between 'Airtime' and 'Standby' because actually using a phone drains the battery more quickly.