Asus Zenfone 4 Pro ZS551KL official Pictures. Asus Zenfone 4 Pro ZS551KL is a Smartphone of asus. The Asus Zenfone 4 Pro ZS551KL Android Smartphone. Announced Aug 2017. Features 5.5″ Display Snapdragon 835 Chipset Dual: 12 MP (f/1.7 25mm 1/2.55″ 1.4µm 4-axis OIS Dual Pixel PDAF) + 16 MP Primary Camera 8 MP Front Camera 3600 MAh Battery 128 GB Storage 6 GB RAM Corning Gorilla Glass 5. Asus Zenfone 4 Pro ZS551KL price starts.