T-Mobile has become the latest US carrier to apply for experimental licenses from the FCC, after requesting approval to test prototype equipment in the 2.7GHz and 4GHz bands.

In a filing to the Federal Communications Commission (FCC), as noted once again by Steven Crowley on X, T-Mobile has sought to test the two frequencies just days after Verizon filed to test 4GHz midband spectrum for potential 6G use cases.

In the application, dated September 17, T-Mobile told the FCC that it plans to test the 2.7GHz spectrum band at a total of seven sites, including six in and around T-Mobile’s headquarters in Bellevue, Washington, and one in Kirkland, Washington.

T-Mobile said it wants to test this band for a period of two years, from November 16, 2026, to November 15, 2028.

The carrier added that it's in the "public interest" that it's allowed to test this band, as it "will enable T-Mobile to conduct critical research and development activities that will support the advancement of wireless services without causing harmful interference to others."

"It will also generate valuable data regarding coexistence with in-band and adjacent-band users, including federal radar systems and radio astronomy operations," T-Mobile said.

According to the carrier, testing will create up to seven temporary fixed base stations, with each base station operating with up to six experimental devices. T-Mobile added that no new towers will need to be built, nor will any of the antennas be installed more than six meters above any existing structure.

The FCC is set to auction off 2.7GHz spectrum in 2028, a year after it plans to host a C-Band auction.

Meanwhile, T-Mobile is also looking to test prototypes in the 4.8GHz to 4.9GHz portion of the 4GHz band for the next two years, until the end of October 2028.

Unlike Verizon, which named vendor partner Ericsson in its application, T-Mobile didn't specify any vendors.