My experience has been less then ideal with this application (iOS). Often calls do not establish or the call get dropped within a few minutes. WhatsApp (voice)

My experience has been less then ideal with this application (iOS). Often calls do not establish or the call get dropped within a few minutes. WhatsApp (voice) on the other hand as not exhibit any of these symptoms when communicating with the the same parties using the same devices and networks. Does anyone else experience this? I do wonder if there is an ISP or operator involved in degrading / blocking the service.