In the commentary of the developers writing to each other, they state that they are setting the caller ID differently from the truth, because if they call somebody it gives them the ability to have the person calling back on that number be routed to a different line. That could either be a voice mail message or something else—just not the same number that actually called them.
That is a problem as far as the U.S. side of things is concerned, because it is my understanding that the ability to do that is highly restricted to law enforcement situations, at least here in the U.S. Here, anybody spoofing caller ID information could face a lot of penalties, at least if it's aimed towards Americans. I'm not an attorney or a prosecutor, but that's my understanding.