Hi, I bought the game at launch and recently started playing again.
I've just got my friend to download the Free-To-Play version.
What I need to know is, can he buy a game time card or subscribe whenever he wants and get full privileges or does he still need to buy the full game with a product/registration key?
He does not need a product key since the game is now free, though he can certainly buy the game if he wants and get the free 30 days subscription. If he wants to be a subscriber without buying the game, all he has to do is buy a subscription using a GTC or credit card. Also, after doing either of these (from my understanding) if he decides to unsub, he will be at preferred status instead of free.