{ config
, lib
, pkgs
, ...
}: {
  config =
    lib.mkIf config.hardware.librem5.audio
      {
        services.dbus.packages = [ pkgs.callaudiod ];
      }
    // (
      let
        paConfig = {
          enable = true;
          # this is required to correctly configure the modem as PA source/sink
          extraConfig = ''
            .include ${config.hardware.librem5.package}/etc/pulse/librem5.pa
          '';
        };
      in
      if lib.versionOlder (lib.versions.majorMinor lib.version) "25.05"
      then {
        assertions = [
          {
            assertion = config.hardware.pulseaudio.enable;
            message = "Call audio on Librem5 requires pulse audio to be enabled through `hardware.pulseaudio.enable`.";
          }
        ];
        hardware.pulseaudio = paConfig;
      }
      else {
        assertions = [
          {
            assertion = config.services.pulseaudio.enable;
            message = "Call audio on Librem5 requires pulse audio to be enabled through `services.pulseaudio.enable`.";
          }
        ];
        services.pulseaudio = paConfig;
      }
    );
}