iOS/Azure Messaging App

I'm pretty new to iOS development, and am wanting some hints as to how to proceed with a custom messaging app I need to develop.

The app will allow me to do simple (JSON) messaging between any two persons or devices on the system.

I think MS Azure has the features I need, but I'm not sure how to go about it. I'm absolutely sure iOS has the features to help me - but again, I don't know enough to look in the right places.

Any hints .... I'm writing in Delphi/FM - but I don't think this is a language dependant question.