Question: I have been using android c2dm push notifications for my app, but since Google is going to stop c2dm I need to know how fast I should move all my users to android GCM so as to avoid any problems faced by my app users.

Answer: 
C2DM has been officially deprecated as of June 26, 2012. This means that C2DM has stopped accepting new users and quota requests. No new features will be added to C2DM. However, apps using C2DM will continue to work

<https://developers.google.com/android/c2dm/>

GCM is the right option for you.

Google Cloud Messaging for Android (GCM) is a service that helps developers send data from servers to their Android applications on Android devices. This could be a lightweight message telling the Android application that there is new data to be fetched from the server (for instance, a movie uploaded by a friend), or it could be a message containing up to 4kb of payload data (so apps like instant messaging can consume the message directly). The GCM service handles all aspects of queueing of messages and delivery to the target Android application running on the target device

This document describes how to write an Android application and the server-side logic, using the helper libraries (client and server) provided by GCM.

Check these links,

<http://developer.android.com/guide/google/gcm/gs.html>

<http://developer.android.com/guide/google/gcm/demo.html>

<http://www.basic4ppc.com/forum/basic4android-getting-started-tutorials/19226-android-push-notification-gcm-framework-tutorial.html>

<http://fundroiding.wordpress.com/2012/06/29/google-cloud-messaging-for-android-gcm-simple-tutorial/>

for client side app you can find the code here

<https://github.com/marknutter/GCM-Cordova>
Google has announced end of life for C2DM notifications. The end of life date is July 30, 2015.

Found on the [C2DM home page](https://developers.google.com/android/c2dm/):

> 
> Important: C2DM was officially deprecated on June 26, 2012, and will
>  be shut down completely as of July 30, 2015. Existing C2DM developers
>  are encouraged to migrate to [Google Cloud Messaging for Android](http://developer.android.com/google/gcm/index.html) (GCM).
>  See the [C2DM-to-GCM Migration document](http://developer.android.com/google/gcm/c2dm.html) for more information.
>  Developers must use GCM for new development.
> 
> 
>