Engadget reports that the game Easy Piano for the Nintendo DS will launch in November in Europe and Asia. There is no US launch date yet.

• 8 note piano keyboard peripheral
• Requires GBA slot, so only works on the classic Nintendo DS and not the new DSi
• Includes 40 songs, such as Bohemian Rhapsody, Bittersweet Symphony, Every Breath You Take.
• Lesson mode and mini-games for learning to play the piano
• Creation mode allows recording up to four 3 minute songs

There have been arcade piano games, like Keyboard Mania (scroll to bottom of that post for video). But actual fake plastic music games with keyboards are somewhat rare.