The update which is still in beta for Android version 2.16.189 is getting call back and voicemail feature. With this new feature, when someone calls you on WhatsApp and you decline or cut the call, you will get a new screen showing three options – cancel, call back or record voice messages.
As the name suggest implies, the Cancel option cancels the whole process.. The Call Back option allows you to call back. This saves the stress of going back two windows to call again. While the case of the voice mail shows up as a regular voice message to the receiver.
In order to record the voice mail you will be required to tap and hold on the ‘mic’ icon just like the way of audio message. After recording the voice message it will be shown in the chat conversation between you and the recipient.
WhatsApp is currently testing the feature only with beta users and its unclear when the messaging service provider plans to bring the option to more stable builds. To try out this feature in the beta mode, you can Sign up for whatsapp beta program