Sprint has been negotiating with Deutsche Telekom to buy T-Mobile USA in what would be a major shakeup of the US Cellular industry, sources alleged on Tuesday. The discussions hae been cast as "on and off" due to a dispute over how much T-Mobile would be worth, but the pursuit has raised the prospect of DT having a formal stake in the resulting union. The German company would own about half of the unified firm in this strategy, Bloomberg heard.