How dual 4G VoLTE works for UMIDIGI devices?

How dual 4G VoLTE works for UMIDIGI devices? />
The UMIDIGI A1 Pro takes advantage of a modern 5.5-inch 18:9 aspect ratio display with 1440 x 720 resolution. It boasts an 85% screen-to-body ratio. UMIDIGI A1 Pro powered with MediaTek MT6739 processor, aided by 3GB of RAM and 16GB of internal storage. read more