When someone has called my work phone, it's been giving a little ring and then just going to voice mail. So, I decided that I should probably call someone and ask about it. I decided to flip through the section of the "wlecome kit" that has various things about the phones and voice mail. I found a little memo that told me how to activate and deactivate sending calls directly to voice mail. So I deactivated it. I walked over and asked my co-worker to call my phone. I told her my extension. In the 4 seconds between hearing the (4-digit) extension and attempting to dial it, she apparently misremembered it. Anyway, she called; it worked.
When I first got here, my phone was set up for whoever was last here, and apparently someone had gotten tired of the phone ringing and set it to go directly to voice mail. Yes, you don't need a password to do that. You just pick up the phone and hit *3. That would be a fun thing to do to all of the phones late some night.