All existing Google Voice users are now given the ability to port mobile numbers1
Previously, only certain users were given the ability to accomplish this, but now they've extended it to all existing users - with new users getting it within the next few weeks. However, you'll need to dish out $20 to get your number ported over and will take approximately 24 hours to fully complete. In addition, it's a good time to remind those who are trigger happy to remember that you'll incur an early termination fee if you're still under contract, but if not, you're free in the clear to get the process done without any worries.
So if you're still carrying on that first cell phone number you were given, you can gladly bring it to the next level and into the clouds so you can access it on a variety of devices.
source: Google via Phonescoop