WhatsApp Beta for Windows Phone tests new feature that alerts contacts to your new number
Besides relaying the new number to your groups automatically, the new feature allows you to choose from three choices. You can decide to pass the new number along to all of your contacts, or only to those contacts you have chats with. You could also decide not to pass out your new number to any of your contacts. By the way, the new feature is disabled by default.
Of course, none of this means a darned thing to you unless you've installed WhatsApp Beta on your Windows Phone or Windows 10 Mobile device from the Microsoft Store. It is important for you to understand that before installing the beta version, you will have to uninstall the regular version of WhatsApp from your handset. Since many beta versions of an app are not stable, you might have to put up with a version of the app that is not quite ready for prime time.
On the other hand, being a beta member means that you get to see what new features are being tested for the app before any of your neighbors find out. You can quickly check out the app by clicking on the sourcelink.
source: WhatsAppBeta (Windows)