T-Mobile USA, the country’s fourth-largest cellphone carrier, has completed its acquisition of smaller rival MetroPCS.

T-Mobile is adding 9 million MetroPCS customers to its own 34 million. The combined company will still lag No. 3 Sprint Nextel Corp. in size.

No immediate changes are expected for customers of either company. However, T-Mobile plans to shut down MetroPCS’s network over two years, which means MetroPCS phones will eventually stop working. T-Mobile will use the space freed up on the airwaves to boost its own coverage and data speeds.

T-Mobile, a subsidiary of Germany’s Deutsche Telekom AG, will gain its own U.S. stock listing by merging with Dallas-based MetroPCS Communications Inc.

The combined company will be called T-Mobile US Inc. and will start trading on the New York Stock Exchange Wednesday under the ticker symbol "TMUS."