Sprint Corp, Kansas City, Missouri had its senior unsecured debt to triple-B-plus from triple-B and its subordinated debt to triple-B from triple-B-minus by Duff & Phelps Credit Rating Co. The ratings cover some $5,100m of debt. The Chicago ratings agency said Sprint had made significant strides improving the profitability of its long distance division, adding that a critical rating factor was free cash flow being generated by Sprint’s long distance operations which enables the company to reduce its outstanding debt balances.