http://netease.im/
http://www.easemob.com/customer/im
http://www.rongcloud.cn/
https://www.jpush.cn/common/im/
http://www.yuntongxun.com/api/im
App 即时通讯 SDK
原文：http://www.cnblogs.com/zhaoyanjun/p/5578529.html
