In german boards there are several speculations about how the N1's WiFi tethering works and how carriers might detect it. But there are no real facts, it seems like there is no one, who really knows about it.
Maybe here are some kind of "cracks", who really know what they are talking about and can provide some real information about it.
How does N1-tethering work? I guess it uses NAT-routing. Is this right? And the probably most important part: How do carriers detect tethering? They officially claim, they could detect it. But the question is, which way do they do this? Can they only detect if you use tethering at all, or do they also have the ability to separate between tethered data and phone's data? Only in that case they would be capable to bill the tethered data (here in Germany some carriers do not prohibit tethering, they can only charge about 50 cent per MB).
Is it possible, that the carrier only detect several devices, that connect to the internet using tethering? I'm a vodafone-customer and I've tried tethering my iPad and my Linux-Netbook several times. Nothing has been charged. Other customers, having the same data-plan, reported, that they habe been charged for tethering within minutes.
Maybe someone can answer my questions.