Chat application

We are looking for a Whatsapp kind of application with much lesser features. We don’t need Mobile Application, we just need the server side application and apis for enabling the chat feature on our existing Android and iOS Application. Only companies/Free lancers who has a production ready solution should apply. Project award and payment immediately after testing the solution and a technical evaluation.. Features should include: Private chat, Group chat and Image posting. Should have Apis and sample code for both iOS & Android App. Support till we integrate the chat feature completely. Public chat rooms in which anyone can join.