Approximately 7,000 customers across New South Wales were reportedly affected by a technical error which saw them receiving calls not intended for them.

"On Tuesday, technical staff identified an error in a database that is used to direct NBN voice calls. As a result, some Telstra NBN Voice customers in NSW were unable to receive incoming calls as the database incorrectly directed these calls to another number," a spokesperson for the telco said on Friday.

"Telstra apologises for the inconvenience this has caused to our customers."

The incident was first reported by ABC News.

Since the incident on Tuesday, 130 customers were still experiencing problems with their Telstra NBN voice services and only had their correct phone numbers restored in the past 24 hours.

"Most of these services were restored on the same day but the remaining few were restored yesterday," the spokesperson said.

As more and more consumers make the switch to the NBN, Australian Communications Consumer Action Network (ACCAN) is calling on Telstra to ensure that its older network is maintained so that consumers using that network get the same prompt service as those using Telstra NBN. Whilst ACCAN congratulated Telstra on its prompt action on Tuesday, they said in a statement today that they are concerned further issues have been reported.

Telstra have confirmed that customers will not be charged for voice calls made by these numbers for the duration of the incident.

The issue is likely to get more complicated as NBN begins its ramp up of the fibre-to-the-node deployment of the NBN which will utilise the existing copper network for services at the same time as ADSL services are connected.

NBN this week said it would only guarantee 12Mbps download speeds for customers on the fibre-to-the-node service in areas where the transition to the NBN had not yet been fully completed.