Get the SENDER_ID

Go to https://console.developers.google.com

1) Look for Utilities and more close to the user profile.

2) Go to Project Information.

3) Copy the numeric value (not the string) of the Project Number field.

Create the sending key

Go to https://console.developers.google.com

1) Go to API Google Cloud Messaging -> Activate

2) Create credentials

Select 'Web server'
    Name: <Proyecto>-GCM
    IP:
Create

3) Copy the key

Installation

_$: cordova plugin add phonegap-plugin-push --variable SENDER_ID=<Project ID>

Note: This plugin does not work with phonegap serve so you must create an apk application and install it on your smartphone after every change. Or use an emulator.

Include the plugin

.../phonegap/config.xml:
------------------------
...

<!-- Plugins -->
<plugin name="cordova-plugin-whitelist" version="1" />
<plugin name="cordova-plugin-inappbrowser" version="1" />
<plugin name="phonegap-plugin-push" />

...