WhatsApp has announced that it would not be supporting for a number of older platforms such as Nokia's S40 and Symbian OS, Android 2.1 and 2.2 Gingerbread, and BlackBerry OS including BlackBerry 10 by the end of 2016.
The decision by WhatsApp to drop support for these OS doesn't come as shock considering that devices running these OS are no longer being produced with the exception of BlackBerry 10, which BlackBerry may or may not be making.
WhatsApp says that ending support for these OS will allow it to focus its efforts on the mobile platforms that the majority of people use. I for one think that the small team of engineers behind the WhatsApp instant messenger have done a great in supporting a large variety of platforms.
Source WhatsApp blog