WhatsApp started out as the de facto standard in cross-platform mobile messaging applications. BlackBerry had its BBM, Apple came out with its iMessage and there were the likes of Skype and Google Talk on most devices, but no truly cross-platform application has seen such widespread adoption as the WhatsApp messenger. With popularity, of course, came the public scrutiny and over the years, the application's reputation has been marred by reports of malicious spam, encryption errors and privacy concerns. And as of February 2014 came the announcement that Facebook, the privacy-embattled social networking platform, was acquiring WhatsApp for an unheard of $19 billion US dollars and with it came more privacy concerns stemming from suggestions that Facebook was paying this much to gain access to millions of actual user phone numbers, which WhatsApp has been using in lieu of usernames in their application.
How to delete your WhatsApp account?
If you decided to remove WhatsApp from your devices over possible privacy concerns, please note that simply deleting the WhatsApp mobile application from your smartphone does not delete your account. It leaves your billing information, phone number, contacts and message history on WhatsApp (soon to be Facebook) servers. In order to purge some* of that data first, use the following steps to make sure your account is deleted, before you uninstall the application:
Open WhatsApp, go to WhatsApp Settings > Account > Delete My Account.
Open WhatsApp, press the Menu Button > Settings > Account > Delete My Account.
Open WhatsApp, swipe down from the top and go to Settings > Account Info > Delete My Account.
Open WhatsApp, tap the three dots on the bottom and go to Settings > Account > Delete Account.
For additional details, refer to the WhatsApp FAQ article on how to delete your account.
If you still want to continue messaging your friends on your mobile devices without paying through the nose for the SMS fees, consider Skype or BBM as free, more privacy conscious, cross-platform messaging alternatives.
* WhatsApp does not actually offer any means to purge your data from their servers. Deleting your account is as close as you can get, and according to their FAQ, it only removes you as a contact from your friends' lists, deletes the message history from your phone and deletes your payment information from their servers. I've reached out to WhatsApp support for a way to delete my data from their servers but did not receive an immediate response to my inquiry. Will update the post if I hear back from them.