Workers at the bogus call centre in Swansea tricked around 3,000 mobile phone users across the country in the eleborate scam.
They targetted people who had just bought phones from Phones 4U and Carphone Warehouse as one of the gang had worked for both companies which meant he had 'insider information' about how the system worked.
They pretended to be from phone giants O2 and Orange - and claimed to offer their customers discounted insurance packages. But a court heard they were not authorised to sell the policies which were worthless.
Prosecutor David Elias said: 'Around 3,000 people across Britain were conned in the fraud.
'It contributed to the erosion of confidence in the industry by members of the public.'
The team, based in Swansea, were monitored by police who installed hidden microphones and cameras to take hundreds of hours of footage over two months.
Craig Pitman, received a suspended sentence for his part in the £300,000 scam while Wayne Ghosh, who was said to have played a leading role was handed a three-and-a-half year sentence
Swansea Crown Court heard how they told customers they were saving money when they paid a one-off sum of £105 to swap their legitimate phone insurance for worthless ones.
Three members of the team admitted conspiracy to defraud, another four admitted selling insurance when unauthorised to do so.
Christopher Surman, of Sketty, Swansea, who was described as the major player, received a four year sentence.
Andrew Patterson, of Swansea, had 'inside knowledge' from working at Phones 4U and Carphone Warehouse. He was given three and a half years in jail.
Wayne Ghosh and Omar Mapara of Bristol, who were said to have played a leading roles in the scam, were sentenced to three and a half years and three years respectively.
Managers Helen Lewis and Craig Odger and Craig Pitman all admitted a charge of selling contracts of insurance which they were not authorised to do and were were handed suspended sentences.
Detective Inspector Dave Runnalls of the South Wales Police Economic Crime Unit said: 'This large-scale investigation into the fraudulent sale of mobile telephone insurance from a Swansea premises identified victims throughout the United Kingdom.
'It has been a long and complex criminal investigation over several years conducted by the South Wales Police Economic Crime Unit and the guilty pleas reflect the overwhelming amount of evidence gathered against the individuals concerned.'