I just saw some scans from Adventure Comics #397, where Supergirl teams up with Wonder Woman. However, of interest is that a couple of times during the story, Supergirl uses super-telepathy to get information from people. Was this some power she had temporarily, or was it simple an editorial mistake?
In Justice League of America #75 BC's sonic blast is said to be generated by her brain, so the idea there isn't too out of line. I don't know when her cry was first represented as coming from her throat. For a period she rarely used it. You'll note there's no mention of it in the Alex Toth two-parter from Adventure Comics. In Justice League of America #110 she "throws back her head-- and sings" for "the first time in many months", but also talks as she's doing it (unless she breaks off singing to talk).
Philip Portelli said:
After checking Michael Fleisher's Encyclopedia of Comic Book Heroes: Volume 2 Wonder Woman, it seems that anyone can send a "telepathic message" but you need the mental radio to receive it!
And the only people who had a mental radio in America were Wonder Woman, Etta Candy, Steve Trevor and, *ahem* Diana Prince!
Thanks for the clarity, Philip! That's sort of how actual radio works -- broadcasters broadcast all the time, but you can't pluck it out of the air without a receiver.