Google Voice Now Lets You Use Your Existing Phone Number
The Google Voice Blog announced that you can now use your existing phone number, with limited features, with Google Voice. Technically, I believe this is not considered porting your phone number, but it does allow you to use your existing number with Google Voice.
Google has created a nice chart showing the difference in features between using a Google Voice number or using your own number with Google Voice:
If you decide to use your existing number, make sure to read the FAQs and help documents carefully. Here is a video showing the various features you get with using your existing phone number: