Bloomberg News says the board of Deutsche Telekom AG, the German company that owns T-Mobile USA, is set to vote on the deal Wednesday.
The companies did not immediately respond to requests for comment. The Bloomberg report did not say what T-Mobile would pay.
MetroPCS shares shot up 18 percent on the news, and Deutsche Telekom's U.S. shares rose 2 percent.
The deal would add 9.3 million subscribers to T-Mobile USA's 33.2 million. The combined company would still trail No. 3 Sprint Nextel Corp. in size. But it would provide T-Mobile with access to additional space on the airwaves for wireless broadband services.