Google has historically broken out preloaded Android apps like Gmail and Maps as stand-alone titles so that they don't have to be upgraded in lock-step with the main OS, but its Calendar app typically hasn't had that privilege. The isolation ends with a newly distinct Google Calendar that's treated as just another Google Play download. You'll need at least Android 4.0 or 4.1, which leaves relatively few differences between the download and what's already on your device,
