WhatsApp beta has just picked up an update to 2.16.189 with a litany of new features. First off is the ability to send a voicemail in case a voice call does not go through, or if the recipient declines the call. Earlier, you had to go back to the chat window to send a voice message, but that option is now available directly in the after-call menu, which also offers the ability to call the user back.
You can also send messages in plain text by adding the grave accent symbol (`) three times before and after the message. Doing so will remove all formatting from the message. If you're looking for further formatting options, you can send messages in bold by adding an asterisk (*) before and after the message, italics by adding an underscore (_), and strikethrough with the tilde symbol (~).
There's also the ability to reply to a specific message in a chat window, which was rolled out in the last update. To do so, you have to do is tap and hold a message, and hit the reply button. The changes are now available in the beta client of WhatsApp, and should be making their way to the stable version shortly.