Excuse me for my ignorance, then, but as you were talking about the N900 Mass-storage driver, I assumed it was using some kind of usb host mode in the inners.

My mistake came from reading the guide about usb mass-storage found here: http://www.lvr.com/mass_storage.htm

And specially the following paragraph:

"The mass-storage bulk-only protocol defines how a USB host can send commands and receive responses using the bulk transfers defined by the USB specification."