Sprint Corp. plans to cut an unspecified amount of jobs and about $2-$2.5 billion in costs in the next six months, the Wall Street Journal reported, citing an internal memo.

The wireless carrier has frozen external hiring and all expenditures require the approval of the finance department, WSJ reported, citing the memo sent to staff by the new chief financial officer.

"We have begun an effort to significantly take costs out of the business so the transformation of the company will be sustainable for the long-term," Sprint spokesman Dave Tovar told Reuters in an email.

The company has been under pressure to cut costs because of concerns that it was spending too much to acquire and retain customers.

It is likely that some jobs will be impacted but it was "premature" to discuss the details due to the early stages of the process, Tovar said.

In the race for subscribers, Sprint, which had 57.7 million customers at the end of the first quarter, slipped to fourth place among U.S. wireless carriers, falling behind rival T-Mobile US Inc.