Asus has announced the sale of 20,000 units of its newly launched ZenFone smartphones on Flipkart from Monday. The sale will have all three sets of Asus- ZenFone 4, ZenFone 5 and Zenfone 6 smartphones, available with the retailer's current cashback scheme. Flipkart is Asus' exclusive online retail partner for the ZenFone series of smartphones.