As with other airlines' in-flight WiFi, there will be a fee. Of it, Air France and KLM only say: "During this period, travellers will be able to hook up to the internet via their Wi-Fi enabled smartphone, laptop or tablet PC at a fixed rate, as well as use their mobile phone for sms or e-mail, whatever their travel class." At least for travelers who only want to google the latest news, that basic information will be free via a portal website which may also include "TV channels relevant to the airline and destination information and a unique offer of online magazines."
So far, so good. The only issue we see is getting those 777s outfitted with power outlets at every seat, because there's nothing more frustrating than paying for a flight-long service only to have your laptop/smartphone/e-reader lose battery halfway over the ocean.