Digital radios were introduced to the Wellington district in June 2009, after a contract was awarded to New Zealand company Tait Electronics.
The Canterbury and Auckland areas were also expected to make the switch in time for the 2011 Rugby World Cup, at an estimated cost of $53 million.
Other police districts were expected to make the switch by 2014, but the technology would be the subject of a new tender.
Operations manager Inspector Lane Todd said Southern district police could move from the analogue radio system to digital by mid-2012.
Police stations, such as Omarama and Kurow, which often helped neighbouring stations in Canterbury, would operate with a dual system until the Southern district made the complete switch to digital, he said.
An encrypted system, already used for groups, would be safer for police and gave them "a huge advantage" in catching criminals, as they could no longer monitor police movements.
When the digital system went live in Lower Hutt, seven gang members involved in a burglary were caught red-handed as their analogue scanners were unable to reveal police were on their way.
Apart from equipment upgrade, there would be minimal change for police, Insp Todd said.
Fire Service communications centre director Trevor Andrews said the lower half of the North Island was likely to go digital in February.
Other areas were expected to be rolled out after police.
In addition to encryption, one of the major advantages of the new system was clarity, he said.
St John southern region operations manager Doug Third said the national ambulance sector was taking part in discussions over a future move to digital, which was likely to follow police and the Fire Service.
