According to the announcement made in February:
While these mobile devices have been an important part of our story, they don’t offer the kind of capabilities we need to expand our app’s features in the future.
WhatsApp will still go through with this plan, but there has been some little changes. The original blog post on the official website has been edited and the update reveals that some devices will still be supported till June 2017. Nevertheless, Android phones running Android 2.2 or below, Windows 7 phones and Apple devices running iOS 6 or below still have less than a month. Support has been extended for Blackberry and some Nokia devices.
These are the mobile platforms that would not be supported by WhatsApp in 2017:
Android : Android 2.1 and Android 2.2
Windows : Windows Phone 7
iPhone: 3GS/ iOS 6
These are the mobile platforms to be supported till June 30, 2017:
Blackberry: Balckberry OS and Blackberry 10
Nokia: Nokia S40 and Nokia S60
If you’re using one of these devices, now may be the best time to upgrade