Today I was thinking...that's been a while no post.
Thus here I am showing you how to use your Nokia N900 as a broadband modem with Ubuntu 9.10.
It's as easy as connect it via USB and choOse the "PC Suite mode".
A Wizard should appear on Ubuntu with few easy step to configure the modem with your provider (attached are the screenshots to document the process).
If the Wizard does not appear simply go to Edit Connections... and add a new mobile broadband connection.
Enjoy the screenshots!
Choose "PC Suite mode"
Choose your Nokia N900 as mobile broadband device.
Pick your country.
Choose your provider from the list of known ones.
Choose your plan among Contract, Prepaid and TopUp and Go available for the chosen provider.
You're done, click apply to save the profile.
Give it a name and save it.