I think this issue is similar to https://bugzilla.mozilla.org/show_bug.cgi?id=871467, during the call state, the telephony channel is active and we are unable to hear the notification/alarm channel either, so actually the problem is already existed which we couldn't solve from the gaia side, but still I would suggest we keep the ringer type because that also means the previewing tone will have the current audio competing behaviour, and associated to the right volume that "Ringer & Notifications" used.