This feature was discovered by WABetainfo on the WhatsApp beta for iOS. During regular WhatsApp voice calls, the app appears to display the default chat wallpaper. Even if you choose a different wallpaper for the contact, WhatsApp will always display the default. This is a feature of WhatsApp’s new voice call interface, which makes the UI appear more compact and modern. The new design is quite attractive, especially in group calls. In terms of calls, WhatsApp has added the ability to join calls after they have begun.
