Whatsapp arrived as a free service on android. The app was really fast even in slow smartphone. And uses your cellphone number as id, so it was really easy to know whom was using. I made a lot of people to use whatapp, because it show if you had send the message and if the other person has read. A problem I had with SMS.
And others messengers? (IMHO) * iMessage is restrict on iPhone and Android dominate market share in Brazil. * Facebook Message was only put in a different app latter in the game. And Facebook App is a bloatware, so it is practically unused on slow smartphones. * Skype app was slow and it didn't use your cellphone number, so I had to ask personally. * Gtalk didn't synchronized messages correctly and I never saw someone outside tech people using it. (Hangout fix the first problem).
A few others tried: Kik, WeChat, zapzap (Brazilian messenger). But none has the mass use. Now days, even my gramma is using Whatapp, so it will be difficult to change.
Telegram is increasing the number of people. I had a lot of friends sign up during this blockage.
The Telcos cartel created a lot of "innovations" in Brazil. It is so expensive to call between different telcos, that people have multiple phones with multiple chips each.
But why is it WhatsApp? It's very frictionless. WhatsApp is a drop-in replacement for SMS. You don't make an account. You just download the app, import your phonebook and start messaging people who are also on WhatsApp. It's SMS except it's free, not more not less. My parents (not from Brazil) are on WhatsApp. They don't use any other social network or messaging app (except Skype).
A company gives you their card information and there are a few things on it: the website URL, maybe an email, the address and a phone number, with the WhatsApp icon on the side!
When there are two numbers, they put the WhatsApp icon in one of them. They literally put another company's logo in their own contact info, because of how WhatsApp is so widespread!
Even if you're offline and send a message, it stores it locally and send it when connection becomes available.
Since the majority of WhatsApp users in Brazil have access only to low quality internet connection, this becomes a major issue.
That's interesting. But it makes sense, I suppose.
It's just the vocal minority that push privacy in WhatsApp. But it is good to see Facebook supporting private communication. Apple and Facebook, who would have thought?
WhatsApp introducing Signal-based end-to-end encryption after it was acquired by Facebook was definitely surprising. I guess they can always switch to on-device profile creation :p. I trusted Whatsapp as a separate entity (low costs, yearly fee). Facebook, not so much.
WhatsApp usage seem to have gone hand in hand with increased availability of smartphones (Android, mostly).
I don't remember any other mobile messaging app that had widespread usage before that.
I used MSN Messenger (until MS killed and managed to kill their IM dominance), and pulled shady stunts with my phone (for example calling, saying a word, and immediately cutting connection, calling again... doing this is free for some reason).
If it was REALLY needed, I would use SMS, it was easy to make mistakes there though (a couple times I ended spending 150 USD in a month in SMS, usually in extremely stressful months where communication was essential).
The need to replace SMS was obvious, and I even had a company where I worked ask me to start researching into how to do it (this was in early 2011, I think some similar stuff already existed in US?), but this project never went anywhere.
And a technical note: doing the phone shenanigans I used to, can get you literally banned from the phone line, I was banned about 3 times (you keep your phone line, and can receive calls, but can't make any except to emergency services), but the only reason I had the phone was to do that stuff anyway (this was when I was still in school, and was the only way to communicate with my then SO, since I couldn't afford spending with real calls or SMS, because of how absurdly expensive they were... mind you, they STILL are absurdly expensive).
It could be that WhatsApp was the first to get translated to Brazilian Portuguese, and since I've always used the English version I never noticed. Even if English is taught as a second language in all schools, most Brazilians can't read or write English, so this is a big deal.
(SCNR)
It seems strange to me that 1 app can capture such an overwhelming majority, because it's just a client, of which there have always been dozens if not hundreds.