GV can't automatically set the forwarding on the Galaxy Nexus VZ, you need to register the phone on the Google Voice webpage and follow the instructions. You may have to go into the settings and change the voicemail carrier as well so holding 1 goes directly to GV instead of VZ. You can find this setting by launching PHONE and then menu/settings. It's not on the main system settings like previous version of android.
Sent from my Galaxy Nexus using Tapatalk