I want to make a cool Raspberry Pi thing that will be put in people's cars. What it does is not important, but somehow people must be able to interact with it.

The ideal solution would be that users on the phone simply used Bluetooth to find the Raspberry Pi, and after pairing - automagically their web browser displayed a webpage served from the Raspberry Pi. Or the phone could render an X desktop or VNC served from the Raspberry Pi.

I guess that this is not possible without an app?

If it requires an app:

1. Can Bluetooth trigger an "app suggestion" on the phone?
2. Are there any open source projects for such an app?
3. Are there any generic apps that provides functionality as described (opens a web page after Bluetooth connection)?

Can Bluetooth serve http traffic at all?