To the best of my knowledge you have to have separate subscriptions for each device. At least I always have.
It's nice to be able to create flight plans on your iPhone or iPad and transfer them to the G3X. Weeks before picking up my plane at the factory I put most every conceivalble route in my iPad while sitting in my recliner. Simply pick the one you want and transfer it to the G3X. And while blue toothed any change made on the iPad or G3X will prompt you to accept the change on the other device. For example if you decide to proceed direct to a waypoint not in the flight plan on the G3X you will immediatley get a request to accept the change on your iPhone or iPad.
David Morris
N508DM
Somerset, KY.