I worry about the TV solution for a few reasons...

1) The video signal runs into the box, then out. I have a pretty nice home theater setup, and I can probably guarantee that the video quality would go down going through such a cheap device.

2) I have TiVo, and the last thing I want to see when I get around to watching is the phone numbers of people (and telemarketers) who called while I was out.

I think the giant lighted sign is a better choice. If you don't have a problem with plugging your computer into the phone jack and having it on all the time (as I'm sure we all do), I bet you could write a quick little app to do what you want. I found one site that had a script for having the computer announce the number through the speakers when a call came in. Also, you can probably find any number of LED marquees which would connect to your computer via Serial. Then, assuming the computer is somewhere near your living room (or you have a really long serial cable), you're all set.

Or you could check out this product.

If anybody is interested in the box, look here.