The open source messaging app, Telegram, has been the new rage in messaging for some time now. Its secure and free (including ad free) nature, coupled with support for multiple platforms as well as desktops makes it a far better choice for messaging than most others including WhatsApp.
With group chats of upto 200 people and secret messaging, it beats most others on this count as well.
What makes it even better is that all the normal chat text and data (video, photo etc) is stored on the cloud automatically unlike other such messaging apps. There are no limits on the data sizes.
Telegram identifies you by your phone number, as before, for all the devices you install it on.