[LiweiZ]

Tencent started with OICQ (later QQ), a somewhat ICQ clone, back in 1999. One of the most important factors, if not the most important one, contributing to the wild growth of WeChat in China is almost everyone online has at least one QQ number connecting with acquaintances. I think QQ was not as dominant as now. MSN messenger was quite popular among young middle class. In fact, the two are mainly used by different classes. After the shutdown of MSN messenger and the rise of domestic organizations (my personal perspective though), QQ seems to be the only dominant force in the market.

edit: typo and added: In fact, the two are mainly used by different classes.