环信
http://www.easemob.com/
融云
http://dev.netease.im/docs/index.php
leanCloud
https://leancloud.cn/docs/
网易云信
http://dev.netease.im/docs/index.php
极光IM
http://docs.jpush.io/client/im_sdk_ios/
阿里百川
http://baichuan.taobao.com/doc2/detail?spm=0.0.0.0.FdiIyK&treeId=41&articleId=103398&docType=1
容联云通讯
爱萌sdk
http://docs.imsdk.im/display/dev/iOS+SDK
原文：http://my.oschina.net/wenbobao/blog/520943