According to this interview the addition of the $.99 charge was to slow down growth. He wanted to be sure they could provide a fast, reliable service and was c

According to this interview the addition of the $.99 charge was to slow down growth. He wanted to be sure they could provide a fast, reliable service and was concerned they might get swamped by an influx of users. https://www.youtube.com/watch?v=puVxnKuFarA https://www.youtube.com/watch?v=puVxnKuFarA According to the interview: WhatsApp began as a "status" service. Original iPhone had no background or push notification; user had to start the app to check others' status. When Apple added push notifications to iPhone, they added this to WhatsApp allowing status to be "broadcast". Users in Europe were paying high prices for international SMS. These users saw that broadcast status notications were similar to international SMS, but free. Some of them suggested this to WhatsApp and so WhatApp added messaging. Then the app took off. WhatsApp used FreeBSD, Erlang and SSDs when, according to Koum, everyone in Silicon Valley was using Linux, Apache, MySQL, Perl (LAMP) and HDDs. Compared to others in Silicon Valley, WhatsApp had far fewer servers and employees per user.