The device can be used without 3G or 2G connectivity just like you would have used your N800 or N810, i.e. e.g. connect to wifi. I just did that in Northern Canada. There was no cellular network (any kind) available in Kuujjuaq or Iqaluit. But there was wifi about everywhere and the it was useful despite of not having the cellular connection, all sort of things worked via wifi. The experience was obviously a bit suboptimal compared to what I have in Finland, where everything works all the time and I can stay connected always to Internet and make calls and receive calls.

However, despite of the not optimal experience of just having the Wifi-connection, the old model N810 that I was able to demo there (could not do that with N900 as it was still top secret), e.g. in a Bed & Breakfast place where we stayed. I did notice two things: 1) they had never heard of this form factor devices before. Advanced ufo technology or something and 2) the N810 seemed very interesting device already. I could believe these people who tried N810 would have also liked N900 with just the Wifi there as that is the most mobile experience they can possibly get other than a satellite phone. And Googletalk and Skype were having a importance we have not used to in here in Finland because there is a telephone network here. There that is about the only way to contact people in other countries for example and the device with Wifi would be already exceptional mobility for them compared to just sitting on front of the computer to make their calls. I think even the fixed line phones there connect through through satellite. There are no cables there.