Alan Hush, 68, Adam Sharoudi, 41, Gavin Brown, 48, and Gavin Cox, 60, were convicted by a jury at the High Court in Glasgow following an investigation at health boards across Scotland.
The offences spanning between 2010 and 2017 included bribery, corruption, fraud, theft and other offences under the Proceeds of Crime Act.
Hush, telecommunications manager at NHS Lothian and then NHS Scotland’s video conferencing manager, was sentenced to eight years in jail.
Sharoudi and Brown, directors of Ayrshire-based telecommunications firm Oricom Ltd, were imprisoned for eight years and seven years respectively.
Cox, who held the post of head of IT and infrastructure at NHS Lanarkshire, will spend six years in prison.
Sineidin Corrins, Deputy Procurator Fiscal for Specialist Casework at the Crown Office and Procurator Fiscal Service (COPFS), said: “This is an outstanding result for justice in Scotland.
“As prosecutors, we have shown an unwavering commitment to pursuing and investigating this matter. This was a betrayal of public trust.
“These four men colluded to create a sophisticated criminal scheme. The public will rightly be shocked by the scale of their criminality.
“The scale of this offending against our public health service is particularly egregious.
“The systematic abuse of position by public officials, who accepted inappropriate benefits including cash, holidays and entertainment in exchange for contract advantages, strikes at the heart of public trust.
“It serves as a reminder that procurement processes exist to ensure fair competition and value for public money. When these processes are corrupted, all of society bears the cost.
“The prosecutorial journey has been complex and demanding. It required forensic examination of thousands of documents, hundreds of witness statements, and detailed financial analyses to establish the full extent of this criminal activity.
“The digital evidence, particularly text messages and emails exchanged between the accused, proved pivotal in exposing the true nature of these arrangements.
“This was a meticulous investigation and one which reflects the enduring partnership working between specialist Crown Office prosecutors, NHS Counter Fraud Services and Police Scotland who worked tirelessly over many years.
“Their unflinching dedication to serving the interests of justice, regardless of complexity or duration, deserves recognition.
“The Crown Office and Procurator Fiscal Service has worked closely with these specialist reporting agencies to ensure justice has been served.
“This case demonstrates clearly that those who indulge in corrupt practices for their own personal gain will be brought to book regardless of the time it takes to bring offenders to justice.
“The Proceeds of Crime proceedings that will follow demonstrate our ongoing commitment to ensuring that crime does not pay and that illicitly obtained funds are recovered where possible.”
All four individuals will now be subject to confiscation action under Proceeds of Crime legislation to recover monies illegally obtained.
Brown and Sharoudi were also banned from being company directors for 10 years.