Wechat is way more than just a SMS replacement. You can pretty much run your life on it. In China, you can book hotels, buy train tickets, pretty much everything on it as well.
What I really like about it is you can create different circles of people (kinda of what Google+ tried to popularize and failed) and communicate with all of them at once. A lot of people are part of circles with their grade school friends, with all their relatives (distant cousins too), etc. etc.