The company integration will mean the loss of every fifth job at O2, which currently has 6,700 employees in Germany and is owned by Spain's Telefonica.
Telefonica O2 CEO René Schuster said in a statement that the redundancies would "create a future-oriented organisation that can react quickly to the market" as the companies underwent the process of integration.
Offices in Verl, Dortmund, Frankfurt, Hannover, Leipzig and Stuttgart will be closed, leaving facilities in Munich and Hamburg.
O2 and Hansenet, the company behind the Alice brand, had already announced in August their plans to reduce their number of call centres from seven to four. Three customers centres, which employ some 600 workers will also be scrapped.
Telefonica O2 bought Hamburg-based Hansenet from Telecom Italia in February, paying some €900 million. With 2.4 million DSL customers and 1,200 employees, Hansenet is Germany’s fourth-largest internet service provider.
In the first half of 2010, both companies reported combined revenues of €2.27 billion.