Google Voice, a smart telephony service from the Internet giant, will soon let everyone port their existing phone number – yes, a relict from the past – to the cloud for a fee of twenty bucks.

A number of blogs spotted the new number porting feature in Google Voice this morning that was available to a limited subset of users. Although the feature disappeared soon thereafter, Engadget was able to confirm with Google that number porting is coming soon "in the near future" to all users.

Number porting will break your service agreement with your landline provider, which may, depending on your provider, incur an early termination fee. Once you port your last century phone number to Google Voice, you can easily set it up so incoming calls to it ring any cellphone or landline number you’ve authorized with Google Voice.

Launched in July of 2009 as an invite-only service in the US only, Google Voice took off to a huge start due to a number of advanced telephony features. The service lets you link all your existing mobile and landline numbers to a unique Google number in the cloud. Users can register their Google number for free, as shown in the screenshot on the right. 

It routes incoming calls depending on a custom criteria, lets you send and receive text messages for free and enables free calling across all of continental US, in addition to cheap international calls starting at two cents a minute.

The web interface puts more advanced features at your control, including automated voicemail transcripts, universal voice mailbox, call recording, phone switching during a call, and more.

Last November, after more than a year long dispute, Apple finally approved native Google Voice app for iPhone due to the government pressure which launched a probe to evaluate competitive practices of AT&T, Google and Apple regarding the App Store approval process.