In order to play any game online with an Xbox, you need a Gold Subscription. All "Free-to-Play" means is that there will not be any Subscription Fees like in World of Warcraft; You will not have to pay to play Destiny. You still have to pay your internet provider, Light bill and Taxes and if you're not on a PS3 (Assuming PS4's really do make you pay for PS+) you'll have to pay for your console's internet access. That should cover any further questions.