I believe the contributors here who testify they heard her say it was a phone call. That's not hearsay. They are witnesses of an event (her speaking).
I am far more skeptical of "I read it somewhere that she said x or y." I read lots, as do most of all y'all, and I know how things I read get mushed and jumbled around in my brain after awhile.
I have to stand up for Mr. Homm's posts...despite the fact that he challenged my and others' memories from almost 30 years ago! Cheers to you, Mr. Homm. You're entirely right. We can't rely on human memory, regardless of whether we're remembering something we heard, saw, or read. The human mind is faulty. I was sober at the con when I first heard her tell the story, but maybe I've got the facts jumbled up with other things I've heard or read since then. So, we do need to find some archival evidence.
In addition to tracking down whether or not the NAACP event occurred, it would be nice if somebody could dig up a published interview from Nichols where the story was different then than it is now.