If somebody is on broadband, it would be relatively simple to have a bit of software running on the PC so that a very short email sent to it would trigger the transmission of a fax containing an ICAO flight plan to a specified fax number. All you need is e.g. Winfax running. Such an email could come from a WAP phone.
I am going to set this up at our mail/www server at work, for my own use. But I will have a GSM modem there so I can trigger it with a text message. Text messages are the one thing that seems to work just about everywhere in Europe, even airborne.
This is actually even better than FP filing over the internet because most airports don't have public internet access, and setting up mobile internet access on a laptop or a PDA which works pan-Europe is fraught with problems.