Yet another Google product. No, I don't work for Google and I don't own
any Google stock (yet). Google just happens to be a company with a lot
of useful products. I don't know why there are free and when that will
change, but when it does, certain products I would probably pay for its
use.
Having said that...
Google Voice gives you a single phone number that rings all your
phones, saves your voicemail online, and transcribes your voicemail to
text. Other cool features include the ability to listen in on messages
while they are being left and the ability to make low cost
international calls. You can record custom greetings for your favorite
callers or block annoying callers by marking them as spam.
At a minimum, Google Voice allows you to give one telephone number to
your callers and have that one number router to wherever you are.
Example #1: You live in two states and have two sets of callers who don't dial outside of their state.
Soultion: Assuming you have a land or cell line with the area code of
state A, get a Google voice number with the area code of state B and
give that number to those who live in state B. Program your Google
voice number to forward the calls from state B to the physical phone
you use which might have the area code of state A, which is irrevelant
to the caller because he/she has a local number to reach you. When you
make a call, you can either dial from the physical phone (state A) or
the Google phone (state

.
Example #2: You have a work cell phone and a personal cell phone.
Solution:
1. Carry the phone that has the best reception and coverage and the
most anytime minutes. Leave the other phone at home, so you minimize
the risk of losng it.
2. Let's assume that your work phone meets this criteria and your
personal phone has limited minutes. Increase your personal minutes by
using Google Voice. Give your personal callers the Google Voice number
and don't give out your personal cell phone number anymore.
3. Call forward your personal cell phone to the Google voice number,
which in turn redirects the calls to the physical phone (the work
phone).
4. Yes call forwarding your personal number will use a minute of time,
but you decide whether to answer the call on your or have Google voice
number leave a caller specific message.
5. You can choose not to call forward your personal number and simply
check for personal messages using either your Google voice number or
your work phone.
Reference: http://voice.google.com