More than 3300 people were ticketed in the first six months of a ban on using hand-held cellphones while driving.
The new road rule came into force in November.
In each of the three months after that, about 450 people were caught using their cellphone.
In the following three months, that rose to more than 600 people per month.
Infringement notices have generated more than $260,000.
Superintendent Paula Rose says police in some areas are noticing drivers are slipping back to old habits.