47 CFR 27.75: Basic interoperability requirement.

(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) 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.

(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.