Let the speculation begin...
According the an interview with Mitsuaki Hagiwara in the latest issue of the Japanese magazine Nintendo Dream, the Nintendo DS includes a port which Nintendo has not yet commented on a use for. The small square port is located on the lower right side of the unit, next to the headphone port. Higiwara said that the hole is not to hold the stylus (this slot is on the back of the DS) and that the purpose of this port will be revealed at a later date.
Higiwara also mentioned that Nintendo is considering releasing the DS in multiple colors. There are no details as to specific color schemes yet, but all the DS systems will be two-toned. Higiwara said that if Nintendo does release the DS in multiple colors, they would appeal to every region of the world, as the system is being released at almost the same time worldwide.