T-Mobile USA has picked Nortel for a $150 million contract to deliver mobile voice and data services and to upgrade the T-Mobile network.

The multi-year agreement is an extension of a current contract between the two companies.

T-Mobile has 26 million customers in the U.S.

“T-Mobile USA’s previous deployments with Nortel enabled us to support more subscribers with a marked improvement in network performance, capacity and call quality,” said Neville Ray, senior vice president of engineering operations for T-Mobile USA, in a statement.