I've been hearing about a service like this for over a decade and only rarely gotten chances to use it or glimpses of the potential.
then came GrandCentral.com, they put the whole package together very nicely.
Let me know if you want a beta invite, it is closed right now.
GrandCentral: The New Way To Use Your Phones
Wow! The whole thing is free right now for basic services, and that includes a banner like the one below that let's you call me, connected by the service!