How can I get that feature? Will it come with an update?This is a known issue that is caused by Microsoft's push servers. We developed a feature that should prevent you from missing your notifications, but we cannot guarantee that this will bypass the issue with the push servers every time you get a call or message.
I don't use WhatsApp so no comment on that but I tried this for Viber. The notification was working fine for a while but then it stopped for some reason...I found if I have any issues with notifications such as this (I've had this similar problem with Viber, WhatsApp, Skype, and a couple others), if you uninstall the app itself (for good measure reboot your phone), then reinstall, notifications will play nice.