This article posits that it was Google Talk (gChat) that caused the exodus from AIM and the other "old" chat networks of the time. In my researched opinion [1][2] it was Facebook (not solely Facebook Chat, but Facebook's entire offering) which did this instead. Quote from my earlier post at [2]:

While it's tempting to accuse AIM, MSN, and Yahoo for being incompetent and not catching up to the "mobile era", they in fact did pursue this market as much as they were able. In truth, early iOS and Android were inferior platforms for a chat app. Push notifications were absent, data rates were expensive, and the average smartphone user at this time was not very likely to use those networks anyway.

Based on this info, I reason that it was truly Facebook that killed incumbent IM networks, at least in the US. Between the release of the iOS App Store and the introduction of push notifications for Android, Facebook grew by more than 300 million active users. This coincided with exodus of users from Myspace to Facebook; many of those users likely having used AIM, MSN, or Yahoo messenger in the past, now found themselves in a much larger network that also offered chat. Since Facebook largely subsumed everyone a person knew in real life, these users only had to go back to the old IM networks to chat with people they didn't know in real life, setting the stage for the weakening of connections and these networks' decline.

By 2010, Facebook, or at least awareness of it, was mainstream. At the end of 2008, the Webster's New World Dictionary named "overshare" as the word of the year, while in 2009, the New Oxford American Dictionary chose "unfriend". For people new to the IM landscape, the old networks were dying and full of "old people" now in their 20s and 30s, so new networks surfacing around this time were appealing. This contributed to the grown of Kik and Snapchat, while people for cheaper alternatives to texting and voice calls drove the adoption of Viber, WhatsApp, and Skype. iMessage went live in late 2011, offering with FaceTime a built-in rich chat on iOS, successfully capturing an audience that would've surely gotten a third-party app otherwise. Later, Hangouts on Android emulated this strategy.

[1] https://news.ycombinator.com/item?id=13952563 [2] https://news.ycombinator.com/item?id=11114518

My friend and I still use AIM everyday. We don't know why people left! Especially with Macs, there's no excuse if you're already using Messages to send texts.

I never got into Google Talk. Too many of the people in my contacts list were either work connections or college acquaintances. And I loathe Facebook so f#ck FB Chat.