It appears Google Voice is gearing up for a mainstream year. For just a few hours between last night and this morning, the Internet giant previewed a feature that's certain to piss off mobile carriers in a big way: number portability.  

Number portability for Google Voice allows users to transfer their mobile number from one service to another, meaning now you can get rid of that pesky landline altogether. 

Er, almost

After TechCrunch and Engadget reported seeing the option go live, it was mysteriously taken down. Here's what Google had to say:

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. 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.

Apparently "limited time" meant Wednesday night and Thursday morning, so unless you're among the lucky few who got to take advantage of it during the tiny window, you'll have to hold tight. Will it be worth it? Jason Kincaid seems to think so:

I’ve been using Google Voice with my primary phone for over a year now, after the team offered to port my phone number over to the service (I was under the impression that it would be released for ‘everyone else’ much sooner than this). My experience has generally been quite positive, save for a series of downtime issues a couple months ago.

NOT a Total Replacement (yet)

NOTE: If you're under contract with your current carrier, you will incur an early termination fee for moving over your phone number to Google, just as you would for moving between carriers. Also, Google is charging a one time US$ 20 fee for transferring your number.  As of now the option only works on non-corporate mobile phones, meaning landlines and your work phone number can't be ported-- yet.

Today Google Voice enables users to make and receive phone calls directly from Gmail, but developments like number porting open up doors for even more convenient communication on top of what's already in the realm of possibility:  making calls from Google TV (which sports Android), from a tablet computer, or any other Internet-connected device. Voice is also a gateway into Google's other services, including the Enterprise, where eliminating carriers and VoIP boxes would be excellent news for small to medium-size business owners.

Currently, Google Voice is only available in the U.S. and calls to the U.S. and Canada will remain free throughout 2011. Voice is expected to roll out to Canada and Western Europe some time this year.

Need more reasons to sign up for the service? Google has ten