Turbine announced today that it's changing the business model for its Dungeons & Dragons Online PC MMO with a new upgrade, due this summer, that shifts the formerly subscription-based game to primarily free-to-play.

Though DDO has existed on a $14.95 per month subscription model since its 2006 launch, the upgrade, titled Eberron Unlimited -- which is itself free -- migrates the game to a microtransactions-based model, by which users can purchase additional content and items in the new "DDO Store."

Specifically, the store's currency is "Turbine Points," and players can either buy or earn them in-game. The new DDO Unlimited will also offer a "VIP Program" as an alternative, through which players receive some in-game money and access to all classes, races, in-game lands and extended character slots.

Existing subscribers are automatically upgraded to VIP status through the update, and free users can join the program for the same $14.95 monthly fee.

"Historically, players of free online games were forced to sacrifice the quality of their experience," says Turbine president and CEO Jim Crowley. "Those days are over. The new DDO Unlimited is the most innovative, exciting and graphically rich MMO to ever hit the free-to-play market and it changes the very nature of what it means to be free-to-play."

The update also includes several content upgrades, including a higher level cap and additional quests. Gamasutra has contacted Turbine for additional comments on the move and will update with any we receive.