WhatsApp will stop working on these popular smartphones this week

WhatsApp has stop working on Windows smartphones on December 31, as well as several Android smartphones and iPhones in the coming months
smartphones on December 31.
You'll no longer be able to use all Windows Phone operating systems after December 31, 2019, and WhatsApp might not be available in the Microsoft Store after July 1, 2019.”
And the end of support doesn’t end there - WhatsApp will also stop working on
several Android smartphones and iPhones in the coming months.

From February 1, people using Android versions 2.3.7 and older will no longer be able to create new accounts, or reverify existing accounts.
due to this versions are old version and they can't meet up the new WhatsApp updrade.
It is advisable to buy new phone with the latest upgrade,
If you want to buy Android phone be sure the Os on the phone start from pie(9.0), if it is iPhone be sure it start from Apple Os 12.8,Harmony Os Android one.