ToplineT-Mobile will buy most of U.S. Cellular’s operations in a deal valued at $4.4 billion, both companies announced Tuesday, the latest billion-dollar transaction by the wireless carrier as it expands coverage to millions of more customers.The wireless carrier will assume billions of dollars in debt as part of the transaction. Getty Images Key FactsThe deal will include a combination of cash and about $2 billion in assumed debt, T-Mobile and U.S. Cellular said in a joint statement. T-Mobile will acquire ...