Windows Phone users who have felt left out of the in-app calling feature recently made available to WhatsApp users on Android and BlackBerry 10 (and soon iOS) can expect the feature too. In an email response to an enquiry, WhatsApp support team had this to say:
WhatsApp Calling for your platform is still in the works. Unfortunately, we cannot comment on any future release timelines but we appreciate your interest in WhatsApp Calling.
How long exactly to wait before this arrives for Windows Phone? Nothing definite for now.