EE is the second network provider this month to announce it would not be working with Phones 4u in the future. Its decision followed Vodafone's decision to sever ties with the retailer a fortnight ago.
Earlier this year both O2 and Three also withdrew from their relationship with the brand.
As a result, the company's 550 stores are closing their doors from today. The fate of the workforce is not yet clear, although staff on the shop floor will not be at work while the administrators decide on the next course of action.
Despite this, a spokesman for Phones 4u's parent company BC Partners announced that "employees will continue to be paid until further notice".
Phones 4u chief executive David Kassler called today "a very sad day for both customers and staff".
"If the mobile network operators decline to supply us, we do not have a business," he said. "A good company making profits of over £100 million, employing thousands of decent people, has been forced into administration.
"The great service we have provided should have guaranteed a strong future, but unfortunately our network partners have decided otherwise."
