The technology package should have been ready to use by more than 700 frontline staff across four major call centres last autumn.
Instead, just as an easy-to-remember freephone number for NHS 24 is due to be introduced, there is still no date for introducing the IT system, which was intended to provide a better service, increase efficiency and save money.
It is the latest in a series of problems to have dogged IT procurement in the public sector - another Scottish health board has recently been involved in legal action over the awarding of an IT contract to a new supplier.
In addition, an experienced NHS 24 worker has written anonymously to an MSP raising concern about shortages of clinical staff covering shifts at the helpline and alleging: "The result of having faith in the new system was that they now have more call handlers who are not clinically trained and fewer nurses."
NHS 24 handles about 1.5 million calls from patients every year. It suffered a crisis shortly after launching 10 years ago when it was overwhelmed with callers.
Since then it has become an integral part of the Scottish Health Service, providing numerous services by phone and the internet.
It is understood NHS 24 began considering a new computer system for managing interactions with patients some years ago. A consultation with staff and patients suggested areas for improvement, including reducing the number of questions callers are asked.
New contracts were awarded to deliver the new system, with BT providing the hardware and international technology firm Capgemini responsible for the software.
According to a source, the system was expected to make calls with patients swifter and give NHS 24 more flexibility to adjust the way it works. The continuing costs of running the technology were also set to be lower, saving money. A move towards expanding the number of calls where patients are dealt with by call handlers, instead of being passed to a nurse, was also anticipated at some stage.
However, the introduction of the system has been delayed after various issues were identified during tests.
Norman Provan, associate director of the Royal College Of Nursing in Scotland, said: "We are aware of the problems NHS 24 has been experiencing in implementing the new call management system and futures programme.
"Clearly, this is something NHS 24 needs to resolve as a matter of urgency. We would urge it to ensure the solution has minimal impact on staff and staffing levels and are happy to work with NHS 24 to achieve this."
Labour health spokesman Neil Findlay has lodged a series of questions in the Scottish Parliament about circumstances at NHS 24 and has called on Holyrood's Health Committee to investigate.
He said: "We know there are concerns about staffing levels from whistleblowers within NHS 24. Now we find out a key IT project that was meant to deliver savings and improve patient care has hit the buffers.
"What we do not know is what additional costs are being incurred by the taxpayers. We do not know how long the delays are and what the consequences for the service are of such delays.
"It is only right that what is happening within NHS 24 is opened up for scrutiny and MSPs have the chance to examine what has gone on.
"We also need reassurance the new system will ensure that people with proper medical training and backgrounds are giving out medical advice to those who are contacting NHS 24."
John Turner, the helpline's chief executive, said calls to the service were being handled safely and effectively and patients should not hesitate to ring.
He added: "In recent years, NHS 24 has been developing a programme to update our technology systems for the future. This will enable us to continue to provide safe and effective services to patients, to enhance the way NHS 24 works by delivering a more streamlined service for patients and staff, and to expand services.
"Our intention is to continue to develop the system with our suppliers and to deploy it when it is safe to do so."
The Scottish Government has lent NHS 24 more than £20m in the past two financial years to prevent the service from going into the red as it has invested in the new system.
A Scottish Government spokeswoman said it was working closely with NHS 24 to resolve the challenges associated with implementing the IT project, adding: "We have provided brokerage to NHS 24 to help avoid additional financing charges associated with the phased implementation costs across the 10-year contract term."
She added: "This will also have no impact on the new 111 number, which will be launched by the end of April."
BT and Capgemini declined to comment.