When you switch to a new phone, WhatsApp usually verifies your account by sending you a six-digit OTP via SMS. But it looks like the messaging platform is working on another method to do so, via flash calls.
According to WABetaInfo, they will allow WhatsApp to call your phone, and then immediately end the call to verify your phone number. The number is reportedly different every time a call comes in, making it impossible to trick.
This feature is being worked on in the beta version of Android 220.127.116.11 update. When it goes live, users will first see an introduction page for the feature. This will explain why WhatsApp will need permission to make and manage calls, and access your phone’s call log. If you don’t like the sound of that, then the good news is that it’s optional. You can still choose to get the OTP via SMS if you prefer.
WABetaInfo also says that this will be an Android-exclusive feature. As such, it won’t be made available on iOS. This is because Apple doesn’t provide any public API for reading the call log. Though this probably isn’t a strong enough reason on its own to justify moving from one platform to another. All that being said, there’s no indication as to when this feature will go live.