WhatsApp is operating on a new feature called Flash Calls in the WhatsApp beta for Android update. Flash Calls will allow users to quickly log into WhatsApp, via an automated verification method over call.

Source: WABetaInfo

According to WABetaInfo: “Using this automatic verification method, WhatsApp will call your phone number and then automatically end the call, verifying the last phone number in your phone’s log is equal to the number that gives you the 6-digit code. This phone number is always different, so there is no way to trick this method, ensuring a safe experience.

Source: WABetaInfo

Points to be Noted:
-This feature won’t be implemented on WhatsApp for iOS: Apple doesn’t offer any public API to read the call history. 

-This feature is optional: you can continue logging into WhatsApp confirming the 6-digit code received via SMS or call.

-WhatsApp won’t use your call history for other purposes: WhatsApp will just compare the last entry from your call history with the phone number that’s supposed to call you. This feature will not be used for other situations.

Currently the feature is under work in progress (WIP) and it will soon be available in a future update on WhatsApp for Android. Click Here to know more