Former heavyweight boxer Julian Gallin was a popular bloke between August and November 2015, when he received thousands of SMS messages asking him to "catch up for a beer."

His network of mates included a former AFL agent, lawyers, stockbrokers, builders and real estate agents, who would regularly contact Gallin at his partner's Elwood apartment.

Julian Gallin, left.

But listening devices and a hidden camera installed by police in the Tennyson Street unit would help explain the flurry of messages to Gallin's phone, which peaked on Friday and Saturday evenings.

Gallin, 34, a security industry manager and agent for Ladbrokes betting agency, was supplying cocaine to hundreds of well-heeled clients in Melbourne's inner-south. He was also under 24-hour surveillance by detectives from the drug squad.