Note 06/10: Using Google Voice to call using Verizon now uses minutes during your prime-time calling plan.
Google Voice is a free data based calling system that gives you a new telephone number, messaging and voice mail services. Calls within the US and Canada are at no charge to your calling plan and international calls are generally pennies (pre-paid) a minute.
GV recently received alot of publicity when it was put on indefinite hold by AT&T / Apple as a service that duplicated or replaced the functionality of the iPhone. It does just that by reducing the cost of calls to the person who owns the phone.
Once your are signed into your GV account on the Droid, it automatically gives you the option of making the call through Verizon or your unlimited data connection. You can set it so that I always goes though GV without the menu appearing.
It's seamless in that you can't tell if you are talking on either service. Those receiving the call or text message will notice a different phone number. You can change your phone number via the GV dashboard at any time. GV voice mail integrates with Gmail though Labs and offers text translation of voice mail.
I recently wanted to return a call from Canada. I haven't had a land line in years. The return call to Canada was free (on a cell phone!) and that is cheaper than it was 10 years ago.
Even if you don't use GV every day it's a great tool for international calls or if you are nearing your calling limit.
It makes me want to actually use my phone for talking.
How is it for calling back to the US when you are overseas?