This generation of Mario Tennis will not support networked or online multiplayer features, Nintendo of Japan has confirmed, following speculation borne of an erroneous update to one of the platform holder's press sites - ironically, organs aimed at informing the assembled e-hacks, rather than confusing them to this degree.
At one point this week, Nintendo's press site featured a listing for Mario Tennis that included reference to broadband adapter support. Compatibility with said adapter wouldn't necessarily guarantee online play, but at the very least it could have meant support for multiplayer over Local Area Networks - a feature touted by both Mario Kart: Double Dash!! and Kirby Air Ride in recent months.
Better yet, as technically minded fans probably know, broadband adapter support in this capacity also opens the doors to unofficial online play - thanks to the various unsupported Cube gateway tools available over the Internet. Warp Pipe, for example.
Sadly though, it was not to be. The broadband adapter support mentioned on the website was apparently a clerical error, and despite a bit of confusion over the page in question (Nintendo killed it, resurrected it, then killed it again according to reports), Nintendo of Japan has now stamped its authority on the situation, issuing a statement confirming that Mario Tennis will not feature either online or LAN multiplay.
Disappointing news, then, but it's our own damn fault for getting so excited. And heck, Nintendo does point out that the game will feature connectivity with the Game Boy Advance! Connectivity! Guys! Come back! Where have you gone?