Karthik Calling Karthik

Karthik Narayan

Ashish

Landlord

(as Yateen Karyekar)

Dr. Shweta Kapadia (as Shifaali Shah)

Young Karthik

Young Kumar

Peon at ACL Office

Secretary at ACL Office

Phone salesman Mumbai

Karthik's mother

Karthik's father

Telephone exchange clerk (as Brijinder Kala)

Hair stylist

Colleague at ACL

Neelu Didi (as Tarana Raja Kapoor)

Siddharth

Man serving drinks at club

Milkman

ACL security guard / Pawn shop clerk

Petrol pump attendant

Bank clerk

Old man at ticket counter

Ticket collector on train

Man on train

Autorickshaw driver

Hotel receptionist

Bellboy at hotel

Old lady neighbor in Cochin

Customer in courier office

Cochin telephone exchange clerk

Phone salesman Cochin

Cochin office secretary

Watchman at Cochin house (as Anand Ekbote)

In an effort to create a more realistic performance for the movie by enriching his acting with the thoughts and emotions of his character, Farhan Akhtar had suddenly withdrawn into a shell, consciously trying to distance himself from the people around, during the course of the film's shooting. Since the part required him to be a lonely brooder Farhan (who is known to be utterly gregarious and accessible) switched off his phone and became almost inaccessible to the world outside. Friends found Farhan's behavior strange since usually he is so reachable and cheerful. For his role, Farhan said "It was the nature of the character I was playing. He's a guy lost in his world. So I was making an effort to isolate myself. Lately I've just been switching off from the world for the sake of my character.If you want to call it method acting, so be it."

Farhan Akhtar's character in the film is apparently shown to be solving Rubik's cube throughout the film. For one scene, he was even required to be shown solving the game in one go.

For the sake of his role in the movie, Farhan Akhtar had taken to solving the Rubik's cube. He became so passionate about it that he solved it wherever he went from parties to shoots to meetings. Since he is known to be a method actor and a perfectionist who believes in going through his paces beforehand, he began learning to unlock the puzzle much before the film hit the floors. He tagged the cube along with him everywhere and practiced it in his free time - in his car, at theaters or even in his office. And reportedly, very soon he became such an expert at it that he now throws challenges at others to beat him at it.

When "Karthik" buys the telephone for the first time, the vendor tells him it's a new Japanese model. The box has Korean written on it (above "Kyungmin Corded Phone") and then the English translation underneath. This is seen more clearly when he buys the same phone towards the end of the movie.