Can I make a Wi-Fi VoIP call on Google Voice without third party applications? I can't seem to make pure Wi-Fi VoIP calls on Google Voice without a third party application such as GrooVe IP. Is this the case?
Unfortunately currently there is no way to make a pure VoIP outbound call via Google Voice on Android.

Previously, you could initiate a free call from Gmail on your PC, then press the * key on the keypad which would transfer the call to all other numbers connected to your GV account, and then you'd pick up the "call" on your cell phone and continue the conversation on your mobile which was still VoIP.  Once Google wised up to this feature being used too widely, they changed this functionality to only allow this transfer for incoming calls only.