Hackett told ZDNet Australia  the launch was about six to eight weeks later than the planned date due to a decision to completely replace the service's core voice switching system with a better one.
While the managing director would not confirm what vendor Internode ditched, he did say the company was now utilising Broadsoft's Broadworks platform.
"The delay will be worth it in terms of a trouble-free result in the long term," said Hackett.
The managing director has for some time been facing online heat from impatient customers who expected the product -- dubbed 'Nodephone' -- in May.
"Our initial selection of vendor and systems turned out to be the wrong one," Hackett admitted in online posts to broadband information site Whirlpool.
"Timeframe estimates for service releases, for all ISPs, are always subject to change -- because they are generally complex and sometimes affected by factors outside of the control of the provider concerned."
Hackett said initial beta tests of Nodephone -- completed in early June -- were highly successful, and the company was now finalising details around training, pricing and support.
"Beta testing has generated feedback which I can only describe as 'excellent'," he told ZDNet Australia .
Telstra -- which has said it would deploy a national Internet telephony solution by the end of 2005 -- said early in March it had commissioned and was testing its own Voice over Internet Protocol solution.