Anecdotally, Skype seems to be the go-to solution for talking to infrequent business contacts. If you don't want to give somebody your personal number or your

Anecdotally, Skype seems to be the go-to solution for talking to infrequent business contacts. If you don't want to give somebody your personal number or your WhatsApp or similar, and they're not on your slack, but you want something quicker than email then Skype is the usual solution. If you suggest some app they don't already know, it might feel like you're inconveniencing your contact. but everybody knows skype and it seems like there's an implicit understanding that if you aren't on skype you should be, so it's always the fallback option for chat apps.