just listen to everything from and after No Diggity. That is definitely a talkbox. It doesnt even sound like a vocoder.
He used to use a vocoder on older guy tracks like teddy's jam.
Just listen teddy's jam 1 and 2 and then listen to teddy's jam part 3.
In part 3 he uses a talkbox and in part 1 and 2 it's a vocoder.