I have an app that currently uses C2DM for push notifications. I would like to inquire if I update the app to GCM and if some users do not upgrade their app, will Google allow me to use both the C2DM and GCM for the two versions of my app?
Or will the users on my previous app never receive a PUSH notification altough I still have the push logic implemented for C2DM?
I've completely replaced C2DM with GCM in the app, and left support for both protocols in the server side. Works like a charm; details are here.