This Apartment Therapy post has a pretty good and simple overview of how you can use your Google Voice # as the number you give your landlord or condo association for your entry in the security phone system. We've never actually had a landline, so we used this for our front door buzzer solution for a good long while.
Why not take it to the next level, though? Instead of having our cell phones ring when somebody buzzes our front door, why don't we fake it to the max and pretend we have a home phone? Back in August, we bought this thing -- an Obihai OBi 100 VoIP Telephone Adapter. What does it do? It connects Google Voice to old school wired telephones. If you've ever know anyone who has Vonage, this is the same kind of deal. A landline phone plugs into this box. You also connect the box to the internet. Log in and enter your Google Voice username and password and boom, you've got a fake landline. Pick up the phone, get a dialtone, dial it like normal, and everything seems to work.
Now when somebody buzzes us from the front gate, our actual landline telephone rings. And when we miss somebody's buzz, we get an email from GV saying "Missed Call from Front Gate." It works pretty slick. We've actually got it connected to one of those cordless phone systems that has multiple handsets, so it gives us a landline phone both upstairs and downstairs.