I found this very helpful software called Voice Plus.
Voice Plus - Android app on AppBrain
The cool thing is it let's you put your contacts into a couple of groups, which tell your phone to use Google Voice or regular outgoing phone numbers, when dialing a phone number.
For example. I use my regular phone dialer to call all my Verizon Wireless Cell phone numbers and use my Google Voice for non-family or friends.
I used to have Google Voice ask me each time I made a phone call, which was a pain. Now even when I use my cars Blue-tooth dialing, Voice Plus will look the phone number up in my contacts and use the correct service to dial out.