The Nokia N810 isn't a cell phone, but it sure feels like it sometimes. With Skype and Gizmo, I can make phone calls to anyone in the world as long as I have an internet connection. This means I can make some incredibly cheap phone calls to anyone in the entire world.
For some people, the Nokia N810 could easily replace your main cell phone. Some areas are now blanketed in Wifi signal which means you always have a connection.
Skype also offers you a number for a small fee which makes it really feel like a cell phone. Keep this in mind when you're thinking about buying a Nokia N810.