Google Voice is definitely a great application and Google has made it even better. Google has just updated the app which includes a feature called "direct access numbers," which now assigns each person you dial a unique outgoing number which now eliminates the need to forward the number to Google's servers. This feature now resembles the process of making a traditional outgoing call.
Here it is explained by Google:
"Until today, the Google Voice app had to make a request to the Google Voice server every time you wanted to make a call to send us the phone number you wanted to dial. Then the call would be connected via a Google Voice access number. With direct access numbers, we assign a unique phone number to every person you call. This means that we no longer need to use your data network to access the server each time you make a call, so calls will be placed much faster."
Unfortunately, Google Voice is currently available to U.S. customers.
Via: Google Voice Blog