My goodness, Throbbingpleasure, you're right! Since you pointed that out I heard Kay's "I'm cumming" during the orgy scene at 45:17, when Starr Wood is being fingered/eaten out by Brooke West. Always thought Starr Wood was exclaiming, "I'm cumming," but that's Kay's voice dubbed over!
That's interesting that Kay Parker's "I'm cumming," was used as a voice-over for other pornstars. I guess she must have made the genuineness of her declaration known to the producers/editors at the time (1979-80), and they and their cohorts wisely used it to make other scenes more credible. I always liked it because Kay, as Barbara Scott, comes off as so prim and proper in Taboo