BT has said it will slash 2,200 staff from its call centres and shut down 53 centres - over half of its current operation unit.
The cuts will take place over the next two years as part of a £100m spend to "create a new generation of multi-function customer contact centres".
The 53 closed-down centres will be replaced by 30 of the "new generation customer contact centres".
The 2,200 redundancies are "included in the figure of 13,000 that we have already declared we will achieve across BT Retail over a three-year period," according to Patricia Vaz, managing director of customer services at BT.
The company said that around two-thirds of current call centre staff will relocate to the new centres and compulsory redundancies would be avoided.
The move follows a four-week period of formal consultation with the unions.
Pierre Danon, chief executive of BT Retail, said: "This is the only way forward if we are to keep our call centre operations in-house and make dramatic improvements to the quality of customer service. Our planned spend of £100 million on this project generates associated savings, giving a two-year payback."
The cuts will take staff numbers in the call centres down to about 13,600.
Currently, each of BT's call centres mostly deal with a specific area of the business. The multi-function facilities would cover a range of services for residential and small-business customers.
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