Word on the street this morning was that Google had quietly made number porting available to all its Google Voice users, but the search giant confirmed Thursday that it is only conducting a test of the option with a few users.

"We're continually testing new features to enhance the user experience. For a limited amount of time, we're making the Google Voice number porting process available to users," Google said in a statement. "We don't have any additional details to share at this time, but plan to offer this feature to all users in the near future."

The service costs $20 (payable via Google Checkout), and basically lets you use your wireless phone number as your Google Voice number. Engadget was among those who noticed the number porting option on its account last night, though the blog says the option has since disappeared. As the graphic below points out, opting for Google Voice number porting will cancel your mobile phone service plan, meaning you could incur early termination fees.

Search Engine Land reports that Google made the number porting move now "because several issues on the back end had been worked out, making it easier to move your wireless number to Google Voice."

Last month, Google added support for the iPad and iPod touch to its Google Voice iPhone app. The update lets users access all the features of the Google Voice app, like sending a receiving free texts, across the three devices.

For more details, see PCMag's "How to Get Started With Google Voice" guide.