1,700 people are to lose their jobs as administrators confirm the closure of 362 Phones 4U stores across the UK.
The failed mobile phone retailer went into administration last week following a decision by both EE and Vodafone not to renew contracts.
The company had more than 700 outlets and 5,600 staff.
Confirming the news Rob Hunt, joint administrator and PwC partner, said: "It is with much regret that we have today made the difficult decision to close a large number of stores.
"It is a very sad day for the staff working at those locations and our thoughts are with them.
"We will make every effort to help the affected staff, working with the Phones 4U HR team over the coming days to support employees."
720 staff have been retained to assist with the closure process, while details of the stores facing closure will be disclosed on Tuesday (23 September) administrators said.
Entrepreneur John Caudwell, who set up the business in the 1980s before selling it for £1.5 billion in 2006, called the conduct of the networks "extremely callous, extremely ruthless".
Vodafone has rejected suggestions that there was any impropriety during negotiations with Phones 4U, while EE said its decision not to renew its contract was driven by uncertainty over the long-term viability of Phones 4U and its strategy to focus on its own shops and cut out intermediaries.
Offering a resolution, EE said it would buy 58 Phones 4U stores, saving more than 350 jobs while Vodafone have purchased another 140 stores, safeguarding 887 jobs.
Dixons Carphone, which is now the biggest independent retailer of mobile phones and network services, have also said it will take on the 800 staff who worked at 160 Phones 4U sites within Currys/PC World stores.