Symbolism, Imagery, Allegory
As far as symbols go, a slip of paper with an address on it probably doesn't seem like much. But imagine you're some guy who's crushing on this girl and you've just given her your number. All of a sudden, that slip of paper is everything. It means a potential for communication—maybe that girl will call you.
That's Mr. Kapasi's view of the slip of scrap paper with his address on it. Here's Mr. Kapasi fantasizing about what the piece of paper could mean:
[Mrs. Das] would write to him, asking about his days interpreting at the doctor's office, and he would respond eloquently, choosing only the most entertaining anecdotes, ones that would make her laugh out loud as she read them in her house in New Jersey. In time she would reveal the disappointment of her marriage, and he his. In this way their friendship would grow, and flourish. (IM 89)
Too bad his fantasies get blown away by the wind (and by the reality of Mrs. Das' personality).