WhatsApp vs iMessage

WhatsApp Messenger is a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for iPhone, BlackBerry, Android, Windows Phone and Nokia and yes, those phones can all message each other! Because WhatsApp Messenger uses the same internet data plan that you use for email and web browsing, there is no cost to message and stay in touch with your friends. Secure WhatsApp alternatives are Signal and Telegram.
iMessage lets you send messages back and forth with anyone on iPad, iPhone, iPod touch, or a Mac. If you’re a texter, you’ll love Messages on iPhone, iPad, and iPod touch. Now they all come with iMessage, a service that’s an even better kind of texting. Because it’s free for you and anyone texting over Wi-Fi using an iOS device or Mac with iMessage.

2015 - iMessage and FaceTime get two-factor authentication to keep up with WhatsApp

Apple has improved the security of FaceTime and iMessage, its voice/video and multimedia chat communication tools. The services received two-factor authentication as an option for users to enable, meaning that even if someone uses their Apple ID email and password to enable iMessage or FaceTime on a new device, they’ll still need to use a PIN from an existing trusted device to gain access to those services. If you’ve previously enabled two-factor for iCloud, it’ll also be enabled to FaceTime and iMessage. The additional level of protection applied to these services helps ensure that people will have a harder time grabbing potentially private images from your iMessage history, or pretending to be you via online communication methods.