Android : Send message from Server to Android device and vice versa

I want to implement a chat application. But I have a few questions, which I could not solve by searching the internet.

My requests are:

• Of course I can address each device individually from my server (makes sense for a chat app)


• I can create a time delay between sending and receiving a message


• The application should not require a registration (this is not a MUST, but would be nice)

I wonder if GCM (Google Cloud Messaging) is the appropriate solution for me. I have not yet worked with it, so I would like to have some help. Will I run into troubles with this? And most important: Is a registration required?