Right after going through the underwater tunnel and going up the steps there will be a talking WAU-ized door button, seemingly in distress and confusion.

If you press the sparking button, you will get zapped and the switch will tell you to stay away from him.

Then he will close the door behind you and tell you to stay here, when you reach for the WAU flower (which will kill him) he will plead for you to stop.

Jane Addams
Vigdis Jonsdottir -> The robot you disconnect to start the plant
Baxter Rogers
Amy Azzaro
Gavin Finley
Louise Meron
Carl Semken -> robot stuck to the conveyor belt.
Aashish Shankar

Isn't that just her body though?

Well, her body has her personality, but if you're referring to Carl having his personality outside his body, no, I don't think that's the case with Amy. She might've been cloned though, but I don't think there's any proof.

I believe I remember that voice sounding most like a male voice.

Yeah the voice is definitely male.
The switch is confused and stressed, saying he has to "get out of here". So I thought about Carl Semken, but his demeanor was much more relaxed when they sealed up Upsilon,and the scan of him that WAU got is from a bit earlier than that even.

Also I wonder how the door switch can talk, it has a speaker for sound, but no cortex chip, unless it's some robot fused with the wall elsewhere, and connected to the door switch.

It's Ross, infact you hear him through a few speakers during the game. Upsilon, Theta, Omicron.
Also.....little tidbit, he's nammed "SATAN" in some of the files and just so happens to be the one telling you the W.A.U. needs to die....food for thought.

Edit: Check some of the old sound files. There's a suit in upsilon that happens to comment "The doors are on our side!"...it's ross trying to guide you.

Edit: Also, forgot to put my reasoning. After listening TO ALL the "speaker" audio files outside of the game, they are ALL of the same, english accent: Ross. He asks you to stay, infacts begs you almost but has no way to hear you at that time. Further into the game you go the more he says to you.

However though, when you touch him, he says "stay away from me", and when you reach for the WAU flower he says "no stop it", which seems like Ross, or whoever is speaking, has his 'presence' in the door button.

When you hear Ross later in the comm center he has a very different demeanor. There he's not stressed out, but very calm and depressed, just telling you to kill yourself because there's nothing left to live for. He doesn't seem at all interested (yet) with speaking to you.