From today going any android user with WhatsApp version 2.12.5 or 2.12.19 can initiate voice calls. Its been in beta test for some months now, but finally WhatsApp for android with above version now access to voice calling.
The iOS version is still in beta test due to Apple tight rules. Though it is long overdue for WhatsApp enabling such feature, Apps like Viber, Wiper,Tango gained voice calling since its introduction. Getting started with the feature is pretty easy. Head over to ‘calls’ tab and tap on the phone icon at the top-right of the screen. There is option to select from the contacts or favorite list and start a new call.
If the updates has not been pushed to your device, wait small to get the latest version. You can download WhatsApp from the playstore if you are new.