We know that Google was considering adding number portability for Google Voice, enabling people to move their currently number to their Google Voice account. That would be a huge plus for the service, and for a time, on Thursday, it seemed it was there, in Phone Setting. Ah, but it was a false alarm.
First noted by Engadget, it turns out the setting was simply a test by Google. It wasn't meant to roll out to end users, just yet. Still, the test means that it will most likely be coming, and possibly soon.
The cost of the service would (and probably will) be $20 to port the number. However, if you are currently on contract with a carrier, that move would cause a cancellation of your contract, and hence, an early termination fee of possibly hundreds of dollars.
The process made it quite clear what was going to happen, though, and users would have to check several checkboxes, and enter their account number, not just their phone number, to make it happen, so it would be hard to accidentally do it. And now that users know this feature is definitely coming, howver, they can start planning if they want to move their number.
Jason Kincaid at TechCrunch has had his number ported to his Google Voice account for over a year (via the Google team). He sees this feature as a major turning point, and we already know that Google has major plans for Voice.
It will be interesting to see how carriers react once this feature rolls out publicly.