Apple is running a special offer on its official India online store. Valid till May 31, the company is giving buyers extra credit on exchange under this. The extra credit or discount is available on both iPhones and Android phones. The extra trade-in credit may range from Rs 3,000 for older iPhones and Rs 1,000 to Rs 4,000 for eligible Android smartphones. This extra amount is over and above the estimated exchange value of the old smartphone. Here we list 20 old iPhones that you can exchange and the amount you will get for them