That means you can switch your mobile number to Google and then just use whatever device you happen to have in your hand to receive calls. That’s an extremely powerful feature for Google Voice.
Outbound calls from those devices will still show whatever phone number is assigned to it, though. But Google has that covered, too. We’ve learned that they are preparing to launch apps for the major smartphone platforms that will automatically route outbound calls through Google Voice. That means whoever you call will see your Google Voice number as the caller.
via Google Voice’s Secret Weapon: Number Portability .
These are great features that may make Google Voice the killer app for telephony. Stay tuned.