The mobile App will only work when it has a stable high quality connection. This means it will work on 4g and Wi-Fi only if there is a good quality connection. If the Wi-Fi has intermittent issues or your 4g signal is weak it might not work. It also cannot roam like a mobile phone, so you cannot move from one connection to another and maintain a continuous call. We recommend using the PC/Mac App when in a fixed location like an office.