Which application software is a cross-platform instant messagingsubscription?

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.