Bob Mansfield resigned as the chairman of Com Tech to avoid a conflict of interest that may arise through his new role as the chair of Telstra.
He said the close relationship between networking specialist Com Tech and Telstra could lead to a "potential possible conflict".
"One of the realities I had to face up to is that with Telstra being one of Com Tech's customers, I couldn't be chairman of both," he said.
"It's going to be very invigorating," Mansfield said of his new role.
Mansfield's four-year term as non-executive chairman at Telstra begins in November. He made the announcement last week at Com Tech's annual user conference.
* Ellen Cresswell travelled to Coolum as a guest of Com Tech.