This app concept is brilliant.
Useful for none: - Volte unable handset or for 4g dongle users.
Like I am having jio dongle so with help of this app I can make calls and receive calls and send sms through my android handset with help of wifi.
And also useful for those whose handset is only 4g lte not volte with help of this app you could make your hanset volte and make/receive calls also video calling available.
This app is little bit slow but over all usefullness is completely life saving.
Layout and design it also quite decent and user friendly.