Those who have played Final Fantasy IX
will vaguely remember a system called "MogNet", in which the player took up the role of carrier between moogles worldwide. There was also something about a purple moogle who used too much hair gel, or something. Whatever.
Anyway, the "MogNet" system will be making a comeback in the updated DS version of Final Fantasy III.
In addition to performing said tasks to unlock various side-quests in the single-player game, players will have the ability to send messages via Nintendo Wi-Fi to other players of the game. Don't instant messages seem a little easier, though? If Square-Enix doesn't implement some sort of in-game incentive, it may be a fairly unused feature.
More details are still forthcoming, says Square-Enix, so keep holding your breath for a party vs. party battle system over Wi-Fi. Oh, how we long
[LOL. GamingBurrito. Awesome.]
[Update 1: Minor grammar issues corrected.]