Hello Sir.
i read through job description carefully and was very interesting to your job.
I have rich experience of chat application.
What kind of SDK used for your original project ?
need to support video/voice call? or only text chat?
Your original project would used XMPP/Ejabberd if only support text chat, I think.
If your project need to support video/voice call, It maybe used webrtc (quickblox, or opentok, or sinch, etc).
Btw, I am very familar with chat application, and also developed serveral chat applications already.
if you want I can show my last apps with source code via teamviewer or the other screen share tools.
Also I can send you source code of my last app, If you want.
I am flexible to work on the other's project, as well as my project.
I will review the source code first 3 days and start to complete it.
I will use git to manage version and will provide daily progress report.
If you choose me, I will deliver high quality app within a short timeline.
Hope to hearing from you soon.
Best Regards
HeNan