I have a ZTE ZXDSL 831AII Ethernet modem which i purchased from BSNL for 1200/- at the time of my DataOne connection. Now I want to switch to a Wifi one which is costing 1600/-(new reduced prices! initially it was 1800/-).. So can i exchange my existing NON-WIFI modem with the WIFI one and give 400 bucks more... is that possible or should I have to buy it at its original price?