I couldn't get it to work either. I have the iPhone connected via Bluetooth, open the ScoutGPSLink app and say connect to my car, click, Toyota, and nothing happens.
Update: I guess it's because if you have the "Entune™Premium Audio w/ Navigation and App Suite", then you wouldn't use Scout GPS... you would use the built in navigation system.
It wasn't stated specifically but I guess ScoutGPSLink only works with 'Entune™ Audio Plus' and not 'Entune™ Premium'.