Regarding ATC (tower/ground) on 121,5... A few weeks ago at Munich airport, a Air Canada
(hopefully a coincidence) A330 was holding for 08L with ground and tower trying to reach them with no luck. Ground or tower even tried on 121,5 so at least in Munich they can
. We were holding behind the Air Canada and eventually got cleared to taxi around them. I tried to wave and tap my headset as a signal to check comms, don't know if it they even saw, but shortly after they did check-in with tower. It might have also been the fact that some pesky regional jet got to cut in front of them that made them wonder what was up, or just sheer coincidence.