Orange has admitted that "technical difficulties" have prevented customers from registering upgraded phones since Tuesday.
The company claimed that a small number of customers upgrading phones "may have experienced difficulties" as a result of the problem.
Orange blamed a technical fault and said that it would be fixed by Thursday evening.
"Orange is committed to offering the best customer service and we very much regret any inconvenience caused," the company said in a statement.
One customer affected by the fault told vnunet.com: "Orange customer services told me the problem affects anyone who has just bought a new phone or upgraded.
"The really annoying thing is they have never been able to say when the problem would be resolved and this has been dragging on for almost two days."
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