Virtua Tennis is going to have not one, but two demos, according to Sega. And both of them will be exclusive to the PlayStation 3 platform - no love for Xbox 360 players unfortunately.
The first demo will give gamers a chance to check out the game's World Tour mode, and it will be appearing on the 13th of April. No release date was given for the second demo, but it will revolve around PlayStation Move and will arrive "when the tennis season reaches its peak."
The actual game is due for release on the 29th of April on both PS3 and Xbox 360. Sega recently announced though, that the PS3 version of the game would have exclusive content.
Source: PlayStation Blog