Puissance Nintendo has interviewed Jim Merrick who describes Nintendo's upcoming online service Nintendo Wi-Fi Connection in detail. An excerpt is below while the full interview can be read here.
Puissance Nintendo: How does it work between Nintendo and the third-party publishers, if they want to use the Nintendo Wi-Fi Connection Service. It will be free for the players, but will it be free for them to bring their games to the service?
Jim Merrick: Yes, it is free. They have the option to charge for their service if they choose to do so. It depends on the game architecture : something like Mario Kart doesn't require servers since the DS speak directly to each other when the match-making is done. It's very low-cost to operate. But a Massive Multi-Player Persistant world-type of game is a very expensive thing to operate: they may decide to charge for something like that, it's entirely their option. But we will not take a percentage of what they charge. That's their business.
PN: Does it mean they will own their own network-infrastructure?
JM: Yes, that's right. But to use the match-making has no cost associated.