More info about the movie, which was written and directed by Spike Jonze:
Set in the Los Angeles of the slight future, the story follows Theodore Twombly, a complex, soulful man who makes his living writing touching, personal letters for other people. Heartbroken after the end of a long relationship, he becomes intrigued with a new, advanced operating system, which promises to be an intuitive entity in its own right, individual to each user. Upon initiating it, he is delighted to meet "Samantha," a bright, female voice, who is insightful, sensitive and surprisingly funny. As her needs and desires grow, in tandem with his own, their friendship deepens into an eventual love for each other.
It's been reviewed very favourably. The trailer: