When Animal Crossing and Fire Emblem were announced for iPhone and Android last month, neither company confirmed the payment strategy the games would adopt for mobile platforms. Nintendo and DeNA's first game, Miitomo, rolled out with a similar free-to-play model where users could end up spending more money in-game on various outfits for their virtual Mii avatar. Although its popularity in the field died down somewhat after initial launch excitement, Nintendo confirmed Miitomo was downloaded and played by over 10 million users worldwide since its debut.
In the original announcement, Nintendo said that Fire Emblem and Animal Crossing were both "pure game applications," especially in comparison to Miitomo's more socially-driven atmosphere. What's still unclear is how Nintendo plans to implement in-app purchases within each game, although it seems that the free-to-play model is a continuation of the company's hope to build up a user base consisting of a wide demographic of players, instead of a purely hardcore one who would be willing to pay outright for each title.
In earlier announcements centering around Miitomo's freemium model, Nintendo mentioned that future games would be pay-to-download, so there's still a chance that the remaining games created between the company and DeNA could be more traditionally priced apps. The rollout plan was already pushed back when Miitomo missed its 2015 launch, but if the company stays on track now, there should still be two more Nintendo apps hitting iOS and Android sometime between this fall and March of next year.