Sprint Corp. and T-Mobile US Inc. have restarted merger talks, Wall Street Journal reported on Tuesday, citing people familiar with the matter.

Shares of Sprint rose 17.3 percent to $6.03, while T-Mobile shares were up 5.5 percent at $63.03.

Both telecom companies did not immediately respond to requests for comment.

The report said it is unclear what terms the two sides are considering, and it is possible, as before, that they could fail to reach an agreement as the discussions are at a preliminary stage.

In November, Sprint and T-Mobile called off merger talks to create a stronger U.S. wireless company to rival AT&T Inc. and Verizon Communications Inc. The companies then said they “were unable to find mutually agreeable terms”.

Japan’s SoftBank Group Corp. owns about 85 percent of Sprint and T-Mobile is controlled by Germany’s Deutsche Telekom AG.