Google announced today that all current Google Voice users can port their numbers to Google. What does that mean exactly? Before getting your next cell phone, port your number to Google Voice. Then get a new cell phone will a new number. You can configure Google Voice to answer the calls and forward it to your cellphone, your computer, and your desk phone. They can all ring at the same time! If you dont pick up at any of those locations, you can also let google take a voice mail, transcribe the message and send it to you via SMS. Your voice mails are also digitized and stored.
http://googlevoiceblog.blogspot.com/2011/01/port-your-existing-mobile-number-to.html