The 26-year-old also calls the film her first love story and her most difficult role so far.
She stars opposite Shahid Kapoor in the movie, which got delayed by a week following objections from Indian Air Force regarding some action scenes. The film will release on September 23 now.
The actress, who is most remembered for her bubbly avatars of Bittu in 'Delhi 6' and 'Aisha', says 'Mausam', set 15-years back, reinstated her faith in love.
"The character is complete opposite of who I am. It is very difficult to say something with just one look or one gesture. This is tough acting. My characters in Delhi 6 and Aisha were loud and had lots of props but this role was difficult," Sonam told PTI in an interview.
"I am a very romantic person and the film, which is about four seasons of love, reinstated my faith love. This is why when I was in Edinburgh, which is the second season in the movie, I felt like I was a part of Emily Bronte's 'Wuthering Heights'," says Sonam.
Ever the romantic, the actress enjoyed the languidness and the innocence of her character in the movie.
"My character in this film has a lot of depth, nobility and subtlety. Every tear and expression says something and if there is a line, it has to convey a wealth of meaning. I was like 'Nutan used to do it'. So I watched all the old movies of Nutan so that I could learn something from her," says the actress.
Veteran actor Pankaj Kapur, who turns director with the movie, set in the backdrop of Air Force, told Sonam and Shahid to write letters and Sonam says it was a difficult exercise.
"It reminded me of our school days when we used to make cards on Rose day and Valentine's day but it was so long back. We have email now which is like SMSes. I did not know where to put 'dear', sincerely or 'lots of love'. I had to relearn it," says Sonam.
Though the actress is part of the tech-savvy generation, she retains a fascination for the old world.
"So much has changed so fast but what is lost is the personal touch. There used to be a lot of thought and little sensitivity but we have become callous, cynical. Technology has given us a lot but it has also taken the humanity out of us," says Sonam.
The actress, who started her Bollywood journey only four years ago, says she does not like doing two-three films together and would rather enjoy each character that she plays.
"I never do two-three films together. My characters in Delhi 6 and Aisha are Delhi girls but I worked hard to make them different. I prefer having female fans because they identify with someone, who is strong, does not care what people think and has an opinion. I don't want to be a show-piece in a movie," says Sonam.