For women, a salwar-suit is also acceptable for business dress.
Jeans with a T-shirt or short-sleeved shirt are acceptable as casual wear in informal situations for both men and women.
You can wear casual dress if invited to a social gathering. However, if a foreigner wears an Indian costume [kurta-pajama for men, and sari or salwar-suit for women], this kind of dress is also appreciated, and often seen as a gesture of friendship.