I am a new Forum and FNB Cell user, trying to figure out what airtime charges is incurred if you have voice minutes and data bundles etc available. Where does the charges for airtime come from, and how is it charged?

When you TOP UP - you can top up the 4 elements: Airtime; Voice; SMS; Data; - Voice is in Minutes, SMS is obvious, so I am trying to figure how DATA and AIRTIME is charged when using a cell phone for internet/email, Whatsupp and obviously calls, and if Airtime is required if you have Data bundles loaded for internet use?