This is what it was on the Millennium in April 2002 (Right from our Cruise Daily):
Guests on the Millennium can now have unlimited soft drinks each day with the purchase of the Guest's Soda Drinks Package. The cost is $4.50 per day plus 15% gratuity. Purchase must be made for the entire length of the cruise. A special stick is placed on your signature card which will allow for unlimited soft drinks at all bars throughout the ship, except Michael's Club, Martini Bar, Champagne Bar, Cosmos Nightclub (after 11PM), Casino or via room service. Replacement stickers will not be given if your signature card is lost. The guest must be present to receive the soft drink.