Google Voice: Can I Make Calls and Receive Them Without Using My Air-time Minutes?

It's tricky, and I have wasted $55 by not understanding this. You always can make free calls to continental US if you place the call from the GV website. But, how about calling from you cell phone?

Scenario: GV Account with GV Mobile Application
If you:

• open a Google Voice (GV) account and add you cell phone number to it
• download to your mobile device a GV application (I'm using Android, G1)
• make a call, or receive, a call selecting Google Voice for this, when asked,  

The call will use your minutes! I have experienced this and it costed me. I know.

Scenario: As Above with myFavs
If you:

• have myFavs or a similar service on your cell phone plan, and 
• you add your GV number to your favs
• receive a call or call you GV voice mail: your minutes won't be used
  
• place call: your minutes will be used

Scenario: As Above with A Twist
If you add to your favs also the number that GV calls when you initiate a call, no minutes will be charged. However, for some reason, this number changes. So, this is not a robust solution.