SEATTLE -- Mariners fans will be learning more than just the names and faces of new players next spring. They'll also be getting used to watching games at T-Mobile Park.
The club announced Wednesday that it has finalized a 25-year naming-rights contract with the locally based telecommunications company. The 47,000-seat, retractable-roof facility had been known as Safeco Field since its inception in 1999, but that naming-rights deal ends on Dec. 31. The Mariners will play at T-Mobile Park through 2043.
Terms of the agreement were not disclosed, but sources have indicated that T-Mobile will pay the Mariners about $3.5 million per year for the naming rights.
The partnership must be approved by the Washington State Major League Baseball Stadium Public Facilities District (PFD), but that is expected to happen quickly, due to the fact that the PFD finalized a 25-year lease extension last week.
The process of replacing Safeco Field with T-Mobile Park signage will take place over the coming months, and most of it expected to be completed by Opening Day on March 28, when the Mariners host the defending World Series champion Red Sox.
The front rotunda of the park and the roof trusses will be lit up at night in T-Mobile's magenta color scheme, and street-level lighting on the outside of the park will be converted to the magenta glow in 2020 or '21, though the inside look of the park will remain largely the same.
T-Mobile is the nation's third-largest wireless carrier. It employs about 6,200 workers at its headquarters in Bellevue, Wash., and a total of about 8,100 in the Puget Sound region.

"T-Mobile Park isn't just some corporate-branded sponsorship to us," T-Mobile CEO John Legere said in a statement. "This is about supporting the community and our hometown Mariners in building a World Series-caliber team."
In addition to the obvious name and signage changes, the ballpark's gathering area for fans near left and center field will be called the T-Mobile 'Pen, which will open a half hour before other gates and include a live DJ on some game days, along with fan giveaways and promotions.
The new sponsor will also host T-Mobile Tuesdays, which will include surprise seat upgrades and free giveaways, plus fast-track entry and discount ticket and merchandise offers at all games for T-Mobile customers.
"T-Mobile has a deep commitment to this community, a passion for customer service and a well-earned reputation as a leader in innovation," said Mariners chairman and managing partner John Stanton. "These are the qualities that make T-Mobile the right partner to name this iconic ballpark."
The recently finalized lease requires the Mariners to pay a minimum of $600 million for ballpark maintenance, operations, capital upgrades and fan improvements over the next 25 years, which will bring the investment of Mariners revenues into the facility to more than $1 billion since its 1999 opening. A minimum of $10 million per year must be designated specifically to stadium maintenance and improvements.
"Fans have come to expect a great experience at this ballpark, and we have made a commitment to invest substantial club revenues over the next 25 years to make sure that continues," Mariners president and CEO Kevin Mather said. "This partnership with T-Mobile will help us meet that obligation so that fans will have a first-class experience at T-Mobile Park for decades to come."