Google Voice, With Your Existing Number, Mobile Or Landline

When I received my Google Voice Number from then GrandCentral, I was very happy because, I will have a number for life, no matter which carrier I use. I now realize that not everyone like to have a new phone number, even when provided with all the services that Google Voice offers.
Now you can use your own number with Google Voice, if you are willing to pass call forwarding, screening, and recording and gain much more than the your carrier offered, like transcribing Google Voicemail.
You can see for yourself the difference of using Google Voice number or your own number with Google Voice.

If you sign up for Google Voice with your existing number, you'll get:

• Online, searchable voicemail
• Free automated voicemail transcription
• Custom voicemail greetings for different callers
• Email and SMS notifications
• Low-priced international calling

But

If you decide to also get a new Google number, you'll get all of the above PLUS:

• One number that reaches you on all your phones
• SMS via email
• Call screening
• Listen In
• Call recording
• Conference calling
• Call blocking

The new feature, could used by people who already have a google number to ease with transition.

Google Voice Blog: Google Voice with your existing number
Google Blog also carries the news
Official Google Blog: Use Google Voice with your existing number