Whatsup is an application software that allows users to send text messages, voice messages, make voice and video calls, and share images, documents, user locations, and other media. Whatsup is a cross-platform instant messaging subscription because it works on different operating systems such as Android, iOS, Windows Phone, and KaiOS, and it requires users to pay a yearly fee after the first year of use. Whatsup uses the user's phone number as the primary identifier and encrypts all communication end-to-end. References: Whatsup - Wikipedia, Whatsup FAQ - About Whatsup, Whatsup FAQ - How to verify your number, Whatsup FAQ - How to access your messages and media.