In or on the elevator

I am going to make up a few similar sentences below.

(1a) Let's get in the elevator.

(1b) Let's get on the elevator.

(2a) When we are in the elevator, we do not talk.

(2b) When we are on the elevator, we do not talk.

Some of my friends think "in" is correct because you are inside the elevator. However, my other friends and I disagree because you usually say things like: get on the bus, you are on the bus, get on the airplane, you are on the airplane, and so on.

Who is correct? Thanks for your help.