Fixed and mobile trailer-mounted cameras around the state nabbed 3303 drivers breaking the law in the seven days after the cameras were activated on December 1.

The world-first technology caught the drivers while checking 773,532 vehicles.

A trial that ran between January and June caught over 100,000 motorists using a mobile phone illegally while driving out of 8.5 million vehicles checked.

Roads Minister Andrew Constance said people needed to understand that driving with a mobile phone is "one of the most reckless and stupid things you can do".

"Not only can you kill yourself, you can kill others," Mr Constance told reporters in Sydney on Tuesday.

"If you look down at 60 kilometres per hour you're going to travel 33 metres in about two seconds. That's a lot of roadway without anybody paying any attention."

A three-month "grace period" means drivers caught using mobile phones will receive a warning letter only until March.

Then drivers will receive a $344 fine - or $457 if caught in a school zone - as well as five demerit points or 10 during double demerit periods.

There won't be warning signs on the cameras as driving while illegally using a phone is "as dangerous as drink driving - it's as reckless as drink driving," Mr Constance said.

Transport for NSW's Centre for Road Safety executive director Bernard Carlon is disappointed so many people are still holding their phone in their hand while driving.

"We just say to everybody, get your hand off it, there's no need to be holding your mobile phone once you're driving your car," Mr Carlon told reporters.

Independent modelling suggests the program could prevent about 100 fatal and serious injury crashes over five years.

"We need to see a steep behavioural change from motorists to save lives," Mr Carlon said in a statement on Tuesday.

Funds from the fines will go into a community road safety fund.

The program will expand progressively to undertake an estimated 135 million vehicle checks on the state's roads each year by 2023.

Australian Associated Press