47 C.F.R. § 27.75

(a)(1) Mobile and portable stations that operate on any portion of frequencies in the paired 1755-1780 MHz and 2155-2180 MHz band must be capable of operating on all frequencies in the paired 1710-1780 MHz and 2110-2180 MHz band, using the same air interfaces that the equipment utilizes on any frequencies in the paired 1710-1780 MHz and 2110-2180 MHz band.

(2) Mobile and portable stations that operate on any portion of frequencies in the 600 MHz band must be capable of operating on all frequencies in the 600 MHz band using the same air interfaces that the equipment utilizes on any frequencies in the 600 MHz band.

(3) 3700-4140 MHz band—(i) Prior to December 31, 2030, mobile and portable stations that operate on any portion of frequencies in the 3700-3980 MHz band must be capable of operating on all frequencies in the 3700-3980 MHz band using the same air interfaces that the equipment utilizes on any frequencies in the 3700-3980 MHz band.

(ii) Starting December 31, 2030, mobile and portable stations that operate on any portion of frequencies in the 3700-4140 MHz band must be capable of operating on all frequencies in the 3700-4140 MHz band using the same air interfaces that the equipment utilizes on any frequencies in the 3700-4140 MHz band.

(iii) Mobile and portable stations that receive equipment authorization before December 31, 2030, and operate on any portion of frequencies in the 3700-3980 MHz band but cannot be upgraded to be capable of operating on all frequencies in the 3700-4140 MHz band using the same air interfaces that the equipment utilizes on any frequencies in the 3700-4140 MHz band can remain in service for the remainder of their useful life.

(4) Mobile and portable stations that operate on any portion of frequencies in the 3450-3550 MHz band must be capable of operating on all frequencies in the 3450-3550 MHz band using the same air interfaces that the equipment utilizes on any frequencies in the 3450-3550 MHz band.

(b) The basic interoperability requirement in paragraph (a) of this section does not require a licensee to use any particular industry standard. Devices may also contain functions that are not operational in U.S. Territories.