What is the fine-grained topic of the following text: WASHINGTON (Reuters) - U.S. antitrust enforcers are in the early stages of reviewing T-Mobile US Inc's (TMUS.O) plan to buy Sprint Corp (S.N) for $26 billion, and have reached no conclusions on how many wireless carriers the country needs, a source familiar with the situation said on Monday. Only return the topic.
U.S. antitrust review of T-Mobile's plan to buy Sprint Corp