You're right re: the JLA communicator.
It must be noted that Hal/GL also sported said JLA signal device despite his omnipotent power ring which could perform the same function.
yes, true... but one must take note that Hal's ring doesn't transmit or receive radio signals to him [or at least not as effecaciously] when the 24 hour recharge period is expended. When the ring is depowered its cosmetic jewelry. Also it's ineffectiveness vs. yellow or other blockers designed to scramble or block the ring's communication aspect that he has encountered time and again.(Including a simple yellow power bubble)
In those cases the JLA signal device is useful. They also allow access to the teleport tubes if i am not mistaken and to the sattelite hq when they had one. Plus the JLA devices where Thanagarian/Kryptonese hybrid technology and supposedly harder for human eavesdroppers to tap into to spy on the League.
I have noted that in the new Millenium Superman his powers are pretty clear. mor e or less, but in the golden and silver age superman, particularly pre crisis/pre monitor age, Superman had all manner of powers , super memory, hypnotism, in the movie Superman 1, hypnotic kiss, element analysis vision, and many more . In the tv series with George Reeve he could phase through walls like the Flash.
I wonder if anybody has ever listed all the powers Superman has exhibitted, not including ones he only got temporarily from Red K or the like.