WASHINGTON, April 25 (Reuters) - The U.S. Federal Communications Commission said on Thursday it will approve the T-Mobile US Inc deal to buy Ka'ena Corp, the owner of budget service provider Mint Mobile, for up to $1.35 billion.

The FCC cited T-Mobile's voluntary agreement to implement a 60-day unlocking period for all Mint Mobile and Ultra Mobile devices activated on the T-Mobile network before and after the closing.

The FCC said the agreement will make it easier for Mint Mobile and Ultra Mobile customers to switch service providers. (Reporting by David Shepardson Editing by Chris Reese)