Google's telephony management application Google Voice is now open to all U.S. residents, as the company on Tuesday removed the requirement for prospective users to receive an invitation in order to sign up for the service.

Already, there are 1 million people with Google Voice accounts. Service features include a single phone number that, when called, rings a person's multiple lines, such as their home, office and cellular phone. Google Voice also offers voicemail message transcription, free calls to the U.S. and Canada, low international calling rates, conference call capability and a central, Web-based voicemail inbox. A subset of Google Voice features can also be used by people who don't want to get the single Google "phone number for life," but rather use one of their existing lines.

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"We're proud of the progress we've made with Google Voice over the last few years, and we're still just scratching the surface of what's possible when you combine your regular phone service with the latest web technology," wrote Google Voice Product Managers Craig Walker and Vincent Paquet in an official blog post.

Google acquired the core Google Voice technology in mid-2007 when it bought a company called GrandCentral. At the time, Google closed new sign-ups for the GrandCentral service. It re-released the service by invitation only in March of last year with its new Google Voice name and a new set of features.

Last year, the telephony service was at the center of a nasty dispute when Apple rejected Google's Voice application for the iPhone, saying that it duplicated native iPhone capabilities.

Google cried foul, characterizing the decision as unfair, but months later found a way around Apple's block by releasing a version of the Voice application for mobile browsers.

Google and Apple are former corporate "best friends forever" now turned rivals, as they compete in more and more markets, such as mobile platforms (Google's Android vs. iPhone), online advertising services (Apple's iAd vs. Google's AdWords), Web browsers (Apple's Safari vs. Google Chrome) and PC operating systems (Mac OS vs. Google Chrome OS).

Google Voice also drew unwanted attention last year when transcripts of some of its users' voicemail messages showed up in search results. Google soon modified the application so that users can continue to share these transcripts on public Web pages, while keeping them out of the reach of search engine crawlers.