We have no way of saying either way how the comm system works. It might show where people are calling from or it might not. Since we don't know, there's no way to say if it's an oversight, silly or otherwise.
As for Parker and Lambert, they get a cart from somewhere, head into a chamber and get canisters from one of the 'copter' ships where Lambert drops some and makes a lot of noise. Then head into another chamber where they eventually die.