Gen-i's new chief executive Tim Miles launched the review after joining the company last month and said an assessment of the New Zealand operations was also underway.
Telecom chief executive Simon Moutter said in February there would be job cuts "well into the hundreds" this year as the company seeks to reduce costs.
Miles said Gen-i had a very successful trans-Tasman business but there were issues of scale with other parts of its operations in Australia.
"If you're going to after substantial business in Australia in the ICT area you need scale to credible you scale to be able to deliver," he said.
The decision to sale back operations was "clear-cut".
"It was pretty obvious to me what needed to happen," Miles said.
Along with its redundancy costs, Gen-i said there would be other restructuring costs associated with the move.