I'm using my N900 with a contract (including internet usage) from Vodafone in Germany.

The details of the contract say that the included data volume must only be used with a mobile phone - not with a notebook which is connected via cable or wireless to the phone.

Furthermore it says that this usage (tethering) will cost 49cent/MB (!!!).

I heard that they can find out if i use my N900 as modem.
There seems to be a "device string" at the connection-establishment which is different if i'm not connecting from the mobile phone. The "mobile phone-string" includes the IMEI number - my notebook sends instead of this an external device code.

Can anyone confirm this statement?

Are there any ways to avoid this horrendous additional cost if i want to use the "flatrate" with another device?
(e.g. "share" a - from the N900 - established connection)

It would be interesting if the use of symbian-tools like juikospot can avoid this additional cost. (I know, there isn't a Maemo-Tool yet, but it is announced)

Thanks for your answers!

I know some ISP that used the TTL from the packets to filter people using NAT gateway but that can be adjusted with a simple iptables rules (I don't know how many of the iptables plugins are supported by the n900 though).

But ... I don't understand why they could see the modem connecting differently if a computer is also connecting through BT/wifi/USB, which can happen even after the modem enables the 3G/EDGE connection.

They could both be there and not serve as a tethering setup but just 2 unrelated activities anyway...