Three out of every four mobile phone court cases are being thrown out in court, with some claiming the item was a Kit Kat, banana or a calculator.

There are 50 fixed cameras set up across the state and countless mobile cameras.

The cameras are catching one out of every 957 drivers using a mobile phone while driving.

Many turn up to court to find a magistrate has a high resolution image of the offence, with the make of the phone often visible.

The string of cases has prompted a warning from Transport for NSW authorities for drivers to stay off their phones.

Drivers caught by a mobile phone detection camera in NSW will be fined $423 and lose five demerit points.

The fine increases to $562 when the offence takes place in a school zone.

Further penalties apply if the driver is caught during a double demerits period.

Revenue raised from mobile phone fines goes into a fund to pay for road safety initiatives.