You may call any phone number, cell or landline, as long as you have an Android or iOS device with an Internet connection (WiFi or 3G). Download the app here.
It is a little tricky to place a call though. First, you need to add the phone # into your phone's contacts, in the International format such as "+862161416222". Don't use "00862161416222", "862161416222" or "02161416222" etc.
Then open the Yixin app, log in, settings, tools, International roaming call or free SMS. Then you can pick up a # to call or text.
The only limit is 60 minutes per month. Other than that, as long as your phone's IP is not recognized as from China, you can call from anywhere for free.
Abstract in Chinese: