At this point there is no way to eliminate voice minutes using Google Voice. Any time you talk on your cellphone, using your Verizon number or your Google Voice number, it will count against your minutes. The way GV works is that when someone calls your GV number, it forwards it on to whatever phone you specify. In this case it would forward it to your Incredible, therefore, it will use your plan's minutes. When you call someone with your GV number, it first calls your phone and then calls whatever person you want to call. So it still uses your cell phone's minutes.
The only thing that GV can save you $$ on is texting. That's because using the GV app to text will be seen by Verizon as using data, and therefore it will be included in your $30-per-month unlimited data plan. So you won't have to get a texting plan on top of your data plan. Unfortunately, if you do a lot of picture/video messaging, you'll still need to use Verizon's plan. That's because Google Voice does not support MMS (picture/video/audio) messaging. Hopefully that's something that's integrated in the future.
Actually if your plan has F&F, with GV you can make and receive unlimited airtime free calls.