As of 2015, Burger King provides coupons for a free Whopper or Original Chicken Sandwich to customers who complete a phone survey after making a purchase. You must have a receipt for a purchase made within the past 48 hours in order to complete the survey.
To complete the survey, the customer dials the number on the receipt. The survey consists of questions regarding the service received during the visit. At the conclusion, the customer receives a completion code that she must write on the back of the receipt. The customer can redeem the coupon for a free Whopper or Original Chicken Sandwich with the purchase of any size beverage and fries.