I know this is a bit further on than what you are suggesting, but it would be great to be able to answer the call on your computer too and have the voices rerouted from your phone to the computer. Similarly being able to reply to an SMS would be cool.

Then I can leave my n900 upstairs charging and be working on my laptop and all my calls/SMS will come to me wherever I am in the house

Maybe it can be semi-achieved with VNC., I'm not sure what happens with sound...