{ lib, cfg, models }:

if cfg.intercomPrefix == null then []
else lib.concatLists (lib.mapAttrsToList (key: phone:
  let
    m      = models.${phone.model};
    ext    = phone.extension;
    # cfg.extensions.${ext} is guaranteed to exist by the phone→extension assertion
    extCfg = cfg.extensions.${ext};
  in lib.optional m.hasProvisioning {
    extension   = "${cfg.intercomPrefix}${ext}";
    endpoint    = "${key}-intercom";
    phoneKey    = key;
    target      = ext;
    displayName = "Intercom ${extCfg.displayName}";
    password    = phone.password;
    endpointTemplate = m.endpointTemplate;
    maxContacts = m.maxContacts;
  }
) cfg.phones)