Reply from Whatsapp Developer,
Hi,
Thanks for your message.
In order to connect to WhatsApp, or activate your number, you will need the latest version of WhatsApp Messenger - v2.8.7 - available from the App Store on your iPhone. Please note that iPod and iPad are not supported devices.
The latest version of WhatsApp for iPhone requires iOS 4.3 or later. Regretfully, Apple does not allow new app updates to be compatible with both iOS 6 and older versions of iOS, effectively ending support for the iPhone 3G. Because of Apple's decision to stop supporting these devices, we can no longer provide new app updates for iPhone 3G users.
If you have an iPhone 3GS or newer device, please update to the latest version of iOS. Instructions for updating can be found at this Apple Support page: http://support.apple.com/kb/HT4972
WhatsApp is also supported on Android, Windows Phone, BlackBerry, and select Nokia devices. Find out more at http://www.whatsapp.com/
So your guys need to blame Apple, LOL.....