The conference room is in a hotel basement, with thick walls & ceilings and lots of marble.
It just struck me to think: could this all be managed using cellular? Leaving aside the issue of roaming costs in Spain, the radio problems alone would be horrible. I'm sure it would be technically feasible given enough effort (eg HSPA macrocell in the corner of the room with 100MB ethernet for backhaul)... but could it ever be provided at a cost suitable for a conference?
It's not just the raw bandwidth capacity either - a pico or femtocell would struggle to deal with the number of simultaneous data connections (PDP contexts etc).
And from a business point of view... how would the organiser contract with all the attendees' various operators to offer "free" coverage during the event? Or would they have to give a separate prepaid 3G dongle to each person, irrespective of whether they already had 3G deal with their normal operator.... and how would the connection manager software deal with that?