After it happend I did check and there are definatly opinions who said it was permissable.
Also even more opinons said it was permitted to salt the ice as well and some said it was only permitted to salt the ice.
And this was even in places without an Eruv.
Hatzolah does have someone man the board 24/7 even on Shabbos and even if there are no calls coming in. Obviously that person could man the board even if no phone calls