title: Smooth GCM to FCM transition
body: <p>Anyone have experience with it? I'm investigating migrating, but as we already have the app released with GCM, with thousands of users and thousands of notifications daily, I'm reluctant for fear of disrupting existing service. Did anyone manage a smooth transition?</p>
  
  <p>Specifically, in the tutorial (<a href="https://developers.google.com/cloud-messaging/android/android-migrate-fcm" rel="nofollow">https://developers.google.com/cloud-messaging/android/android-migrate-fcm</a>) step one is 'Import Google Project'. Is this a one-way operation? Will existing GCM server solution and deployed GCM apps continue to work?</p>
  
  <p>Or is the best bet to create a new project, and maintain two server solutions until the GCM deployed apps are phased out?</p>