I didn’t know these existed, but they seem to be popular. From AICN:
Popular mobile novel (you can only read it by moblie phone through the net) “Deep Love” will make it to the big screen. Michika Shigeizumi won the leading role through an audition of 1600 candidates. It tells the story of a 17 year old high school prostitue who meets lots of people and learns what love is. “Deep Love” is extremely popular among high school students. Yoshi, the author of the novel, will direct the movie as well.