The voice calling feature isn't the new feature added by the update as it brings some nifty features such as:
iOS 8 share extension which allows one to Share photos, videos, and links right to WhatsApp contacts from other apps.
• Quick camera button in chats: Now you can capture photos and videos, or quickly choose a recent camera roll photo or video.
• Edit your contacts right from WhatsApp.
• Select and Send multiple videos at once and also crop and rotate videos before sending them.