Owner of the retail chain, Vodafone, will exit from the Crazy John on 20 February.
Some Crazy John's stores will close, while others will be transformed into Vodafone stores over the coming months.
The telco says its wants to "streamline our retail brand offering to one single brand - Vodafone " and will be closing or rebranding all Crazy John's stores.
"Existing Crazy John's customers will continue to enjoy the value and great service through the Vodafone store network, as well as online, customer care 132299 and mobile MyAccount service," a Vodafone spokesperson told SmartHouse this afternoon.
Vodafone says it wants to prioritise spending to improve its network, and said the surprise move was "necessary to remain competitive."
"We are continuing to focus our investments on our network to provide customers with better mobile coverage and fewer dropped calls. "
"It wasn't an easy decision to make and to ensure we focus our investment where our customers and people will benefit most."
It also hopes to redeploy as many Crazy John's employees as possible to Vodafone stores.