"40 days free" is misleading. I presume you are talking about the 10 day trial + the 30 days gametime. Personally, if I bought the game, I wouldn't waste the trial on myself (I'd give it to a friend or something). As a trial, you cannot use the mail system, you cannot trade with other players, and you cannot use the Auction House. You also have a level 20 limit, which I reached in about 5 days. And don't even get me started on the queues!!! As a trial user, if you're unlucky enough to be queued, you get the lowest priority. I've waited over an hour before as a trial!
In reality, what you get with your purchase is 30 free days, and a 10 day trial key for a friend.