I had a similar issue at an apartment building. I just setup a new Google phone number (with a local area code) and had the number forward to my cell phone, and then to my wife's cell phone if I didn't pick up. So while I didn't have the cool PIN thing, I could let someone in if I was out since it forwarded to my cell phone. I only bring it up because I wouldn't pay for this solution when the free one (which is nearly if not as good) exists.