Retailer Phones 4U has fallen into administration putting 5,596 jobs at risk.
The chain, which is owned by private equity firm BC Partners, said its 550 stores would all be closed on Monday.
Phones 4U blamed mobile network EE's decision not to renew its contract - which came after Vodafone made a similar decision - for the move.
'If mobile network operators decline to supply us, we do not have a business,' said Phones 4U boss David Kassler.
Mr Kassler, chief executive of the firm, said it was a 'very sad day' for both customers and staff.
'A good company making profits of over £100m, employing thousands of decent people has been forced into administration,' he added.
The firm said EE and Vodafone's decisions not to renew their contracts had come as 'a complete shock'.
Phones 4U said it had only received EE's decision late on Friday, and as a result all its employees would report to work as normal on Monday.
It said they would then by briefed by management across all store locations as well as at head office.
It added that all staff would 'continue to be paid until further notice'.
The firm also said all mobile contracts previously bought at Phones 4U would remain unaffected.
It said PwC, which has been appointed as administrator, would decide on whether the business could be reopened for trading.