WhatsApp. How it works? [closed]

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My friend recently downloaded WhatsApp to his Iphone. Anyone can tell me technically how it works? Does it use the same technology as PushMail? How can it stay in the background? I am not a Iphone Developer, btw.

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I haven't used it but it looks like it is using APNS. This allows you to display notifications even though the app is not running

Send a message with text that lets the user launch your app. Trigger audible alerts with your own custom sounds