Win 7 phones home every time it connects to to a network. Microsoft keeps records of your IP numbers. And it doesn’t poll just once, but repeatedly during a session.
The good news is that, not only can you disable the service, you can even tell it to check your own server instead. If you have a server.
But it does seem like quite a lot of work. And they know your IP address anyway every time you run windows update, so the gain of changing all this is limited.
Incidentally, there is a real legal issue here: Microsoft is collecting a huge pile of data that tells it something, more or less reliable, about where users are and how long they are there. I wonder if this is compatible with data protection law in the EU (which I know considered protecting IP numbers as far back as 2008, but I don’t know if this was actually formalized). I suspect this creates a real legal problem in Switzerland.