Hatsune Miku, Len and Rin, Gumi and company probably don't have to worry about the competition too much, but thanks to a concept/tribute album from doujin music IOSYS (makers of Anime House Project), Apple's personal assistant software Siri has become an honorary Vocaloid. With the help text to speech software, "Tell Me Siri-tan!" sings the story of an Apple fan acquiring a new iPhone and spending Christmas with the device he fell in love with - though there is some hardship around the issue of new map software.
By the way, she's showing her back side because "Siri" is phonetically similar to a Japanese word for "buttocks."
Also, worth explaining for the sample below... "ringo" is Japanese for "apple."
The 14 track CD will be released December 8th for 1,260yen ($15.35)