Whatsapp will end the support for Windows phone operating system after December 31, 2019, after which Windows phone users no longer able to create new accounts, nor reverify existing accounts.
Users can continue using it but some features might stop functioning at any time.
Also, Whatsapp will cease the support for Android and iOS versions as below after February 1, 2020:
- Android – versions 2.3.7 and older
- iOS – versions iOS 7 and older
Information from: Whatsapp – Support for operating system