I got it as a promo when i purchased the postpaid number, and it has remained no matter how many times i have changed the plans. It still shows up as Promo Discount on the bill. It was initally, Discount upto Rs.1000. After about 6 months, since i dont sms that much, they changed it to Rs.500 and then Rs.300. But it has remained so for the past 2 years.