Deutsche Telekom’s top two shareholders have told its management that it has until the middle of next year to turn round the German telecoms group’s ailing US mobile phone business.

People familiar with the thinking of the German government, which owns 32 per cent of D Telekom, and Blackstone, the private equity group that holds almost 5 per cent, said they were prepared to force strategic changes if René Obermann, chief executive, failed to revive T-Mobile USA. They added that deals aimed at transforming the business, the country’s fourth-largest mobile operator, were not yet an option.