Google on Tuesday said it has begun offering its Google Voice testers the opportunity to invite friends to join the service.

The company said it will provide three invitations to current users that allow recipients to establish their own Google Voice accounts. The serivce remains in private testing.

Google said that additional invitations will be allotted in the future.

Invited friends may not receive access immediately because the service expansion will be gradual.

The timing of Google's announcement is perplexing: Last week, the Federal Communications Commission began an inquiry into Google's practice of blocking certain high-rate calls in Google Voice following complaints from AT&T and Congressional lawmakers.

In addressing AT&T's complaint last month, Google's telecom and media counsel Richard Whitt differentiated Google Voice from AT&T's voice service in part by stating, "Google Voice is currently invitation-only, serving a limited number of users."

But even if making Google Voice less limited has no effect on the FCC's view of the service, Google still faces the possibility that the government may decide to regulate Internet telephony under the same set of rules that govern traditional phone services.

Google's most recent expansion of the service occurred in August, when the company extended Google Voice invitations to active service members with .mil e-mail addresses for the stated purpose of helping military families stay in touch. It was an act of generosity that also provides political cover: No government agency will want to hobble a service that helps U.S. troops.

Google Voice launched in March and began inviting new users to join up in June. The service provides a single phone number, tied to a single voicemail system, that can be used to ring multiple phones simultaneously. It also provides a variety of other useful communications and messaging features including call screening, online call recording and playback, call blocking, and call notification.

It's weakness -- the inability to make calls using one's Google Voice number from one's mobile phone -- was addressed in July when Google announced the release of mobile apps for Blackberry and Android phones. Those mobile applications can place calls using Google Voice numbers rather than mobile phone numbers.

At the time, Google said it was working with Apple to secure approval for a Google Voice app for the iPhone. But Apple's subsequent refusal to approve the Google Voice app prompted the FCC in July to send letters to Apple, AT&T, and Google seeking an explanation. The agency said that it wanted to gain a better understanding of the situation in light of upcoming regulatory proceedings on wireless open access and mobile handset exclusivity.

In response to that FCC inquiry, Google submitted a redacted letter that the company subsequently published in its entirety. Google's letter contradicted Apple's public account of its treatment of the Google Voice app by stating that Apple rejected the Google Voice app. Apple previously told the FCC that the app had not been rejected and was still being considered.

Google has until Wednesday, October 28, to respond to the more recent FCC inquiry.

Google has said that it hopes to deliver a Google Voice app that runs in the iPhone's Web browser, but it remains to be seen whether the mobile version of Safari is up to the task.

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