Ok, lemme answer it really simply...

The N800 is NOT a phone. It does not connect to any phone network, to make calls or anything else.

The N800 can access WiFi hotspots, which are little tiny areas around a wireless router (like in your local Starbucks) that allow for internet access. You do not need to buy any "service plan" to use WiFi. (WiFi is not a company, btw, just a standard for communication, it means "Wireless Fidelity")

You cannot use the N800 for dial-up internet, or with any wired internet at all (anything that you have to use wires to plug into the wall)

Bluetooth on the N800 is used mainly to communicate with phones that also have bluetooth. Bluetooth can be used to mean hardware or a non-specific software that controls that hardware. This means you can send pictures and music from you phone to you internet tablet (The N800 is called an "Internet Tablet" or "IT" for short).

The N800 is not associated with any phone company. You never need to purchase any kind of plan for any kind of feature on the N800.

Hope it helps!