By Harshita Mary Varghese

Feb 9 (Reuters) - T-Mobile TMUS.O said on Sunday it has started wide-scale testing of its satellite-to-cell service, powered by SpaceX's Starlink, as the U.S. wireless carrier aims to eliminate mobile dead zones and extend connectivity to remote areas.

The beta trial will be free till July, after which the plan will be included in T-Mobile's premium Go5G Next plan at no extra cost. The service can be added to all other plans for $15 a month after its commercial launch this summer.

The move could mark a pivotal shift in mobile connectivity, bridging the gap between traditional cell networks and satellite technology to ensure seamless coverage anywhere on Earth.

T-Mobile said 500,000 square miles of the U.S., which is unreachable by terrestrial cell towers, can now stay connected.

The beta launch will offer text service via satellite, while voice and data features will be added later, the company announced during the Super Bowl game on Sunday.

Customers who sign up for the trial will get a 33% discount when the service is commercially launched, the wireless carrier said.

The service could bolster the company's competitive edge, as its investments to expand coverage, including in smaller markets and rural areas, have driven industry-leading net phone additions in the fourth quarter.

"This is something that nobody else in the U.S. has done, and one of the big distinctive things this network has is that it works across almost all smartphones from the last four years," Mike Katz, president of marketing, strategy and products, told Reuters.

T-Mobile has been working closely with Apple and Google to "ensure that this experience is integrated directly into their OS (operating system), and this will be the default satellite system across both of those phones," Katz said.

The carrier is offering the T-Mobile Starlink service directly to all wireless users, including customers of rival telecom firms AT&T T.N and Verizon VZ.N without having to switch.

(Reporting by Harshita Mary Varghese in Bengaluru; Editing by Shilpi Majumdar)

((HarshitaMary.Varghese@thomsonreuters.com))