Trying to explain to people what Whatsapp really is is really difficult, especially when you have lots of americans going "Hurr durr it's just instant messaging like iMessage, what's the deal?!"
It's used by everyone. iOS, Android, Blackberry, Windows Phone, it doesn't matter.
Your contact point is your telephone number, so it's perfect. Of course you can add your own name, profile photo, status, etcetera.
You can have unlimited group chats. This is the killer feature. I have a group chat for family members, a few groups of classmates, coworkers, small event-related chats for birthdays and get-togethers, etcetera.
Of course, one-on-one chats are just as easy. Just tap the name in your contact list.
It sends almost everything. Share images, voice clips, video's, links, contacts, locations and more with a single button.
It's also customizable with backgrounds, titles and profile images for all groups.
It's really not weird that this service catched on big time. It shits over everything else.