Lkewise, if only for the fact that all the characters would likely have cell phones, which would defeat much of the plot.
Audrey II: Feed me...my branches are so dry.
Audrey: Hang on, let me just check real quick with Seymour. (Dials) Hey, Honey, the plant is talking and asking me to feed it.
Seymour: Get out of there now. Don't listen to it. I'll explain later.
Audrey: Got it...can't wait to hear all about THIS and why I'm only just hearing about this NOW. Bye. (to Audrey II) Seymour says no, so...see ya! (Exits)
Audrey II: Well, DAMN!