Nicholas Nicolaou, 27, and Rajesh Patel, 28, discovered how to trick a BT computer and won more than pounds 72,000 in cash prizes, the Old Bailey was told. They admitted conspiracy to defraud BT and were each jailed for three years.
Mukel Chawla, for the prosecution on behalf of BT, said the two men played the 'Wheel of Fortune', in which competitors were asked questions with yes or no answers.
Nicolaou and Patel, who worked at the New Southgate exchange in north London, discovered that if no reply was made, the computer assumed that was a no answer. When the computer asked if a further question was wanted and no response was received, this was taken to be a request for another question.
After making the first call, the engineers left the telephone lines open for 24 hours a day and won whenever a no answer was correct.