SEGA announced the 360, PS3, and PC versions last week, and today they went on record that a Wii version is also in development:

“Wii owners will finally be able to take to the courts in the fans number one tennis game, boasting all the features and arcade action that has made Virtua Tennis the most critically acclaimed and best selling tennis series available. 

Virtua Tennis 2009 for Wii includes the same impressive player roster as Virtua Tennis 2009 on other platforms, meaning top stars such as Roger Federer, Rafael Nadal, Maria Sharapova and Venus Williams will all be in game, as well as players new to the series such as Andy Murray and Ana Ivanovic. Over 40 court vibrant court environments will be playable within single player, multiplayer and online modes giving Virtua Tennis 2009 an impressive online and offline depth for a Wii title.” 

There was also a rumor that this game could include Wii MotionPlus support, but that’s just a rumor at this point  (The rumor stems from the boxart above where it appears to have a MotionPlus logo near the ESRB rating, although it’s very small to tell what it is).  With the online modes, this could turn out to be a pretty solid tennis game on the Wii.  The game is set to launch alongside the other versions this May.