Although the police were initially satisfied with compliance with the ban, complacency among motorists crept back, and by the end of last year offences were increasing by an average of almost 130 a month - representing about 5 per cent of traffic violations.
But detected offences declined over the first six months of this year.
The police reported to their minister, Judith Collins, and to Transport Minister Steven Joyce that an 11 per cent decrease in the three months to the end of March over the previous quarter may have been partly because extra staff had been sent to earthquake-struck Christchurch.
It may not have been because of better compliance, they said at the time.
But they have reported a second quarterly decline - of 8 per cent to the end of July.
"This decline is largely due to a 9 per cent decrease in offences detected in the Auckland District, which has consistently had the highest level of enforcement in the country."
Detected offences were about three times higher in Auckland than throughout the rest of the country.
National road policing manager Superintendent Paula Rose disclosed plans for the countrywide crackdown in November when she was asked why her officers were so much tougher in Auckland, and whether those in other districts would be given more enforcement resources.
The police ministerial reports also mentioned enforcement campaigns this year in the South Island, including Queenstown, where covert operations were carried out through winter using "spotters" dressed in civilian clothes and in radio contact with patrol cars.
Police drivers, meanwhile, remain exempt from the ban if they use mobile phones in the execution of their duties.
That has concerned some motorists, including a North Shore man who was pulled over by a policewoman who appeared annoyed he had mouthed his disapproval to his wife that she was using a phone while driving over Auckland Harbour Bridge in May.
The incident followed a coroner's finding that month that a Northland police officer ran over and killed a 16-year-old pedestrian 23 seconds after receiving a text from a female acquaintance, although a search of phone records could not confirm he had opened the message.
Another coroner, Carla na Nagara, found last week that a Fastways Courier van driver was texting moments before causing a head-on crash with a truck in Taranaki in January, killing himself.
