Not really in public, but speakerphone is sometimes useful to be able to look something up on your phone in the middle of a call, e.g. checking your calendar when booking an appointment. And if someone called you then you're less in control of whether it's in public or not.
As KRYTEN and LISTER head for the cockpit, the airlock monitor fizzes on
again and a SECOND LISTER appears on the screen.
LISTER 2: What the hell are you doing taking off when I'm still outside?
Let me in.
KRYTEN double-takes between the LISTER inside and the LISTER on the
monitor.
KRYTEN: I'm afraid, sir, you're already here.
RIMMER steps down from the cockpit.
LISTER 1: He's a Psiren -- don't let him in.
LISTER 2: For god's sake -- I can't hang on any longer. He's the
Psiren. Let me in!
RIMMER: What do we do?
KRYTEN: there's no way to tell which is which. We have to let him in.
RIMMER: That means we'll definitely have one Psiren on board. A brain-
sucking psychotic temporal lobe slurper.
KRYTEN: There's a fifty per cent chance we have one on board already. We
can't risk killing the real Lister. I'm letting him in.
It's been this way as long as I can remember down at Moors Valley. From my limited observations there, it surprisingly works much better than you might expect.
I think we made a big mistake coming down from the trees in the first place.