Google disclosed through a blog posting that it will soon be offering Google Voice free to subscribers on its waiting list, extending the advanced VoIP service beyond the original GrandCentral subscriber base. Google purchased GrandCentral in July 2007, adding features such as interoperability with Short Message Service, and it renaming the service "Google Voice" in March 2009.  The service was initially available only to legacy Grand Central customers.

Google Voice include features typically found with other VoIP services such as follow-me/find-me with calls forwarded to one or more phones; call routing based on calling party identity; unified messaging to provide a consolidated and visual voice mail service; call recording; and the ability to seamlessly switch calls from one phone to another phone without interrupting the conversation. Although not a traditional outbound calling service Google Voice does offer toll-free click-to-call/click-to-return call, and calling using a Web-based GUI for U.S. numbers.

Google Voice also offers some features that are seldom found with a basic consumer VoIP service, including advanced services such as speech-to-text conversion (used to create voice mail transcripts); personalized greetings that can vary by caller; the ability to send, receive and store SMS; call screening; and the ability to view an inbox from a mobile phone.

Perhaps the most interesting feature is that Google Voice introduces consumers to the concept of linking a phone number to a person rather than a phone or geographic location -- leaving the user with the ability to manage multiple phones based on personal communications priorities and preferences.

While Google Voice does have some cool call management features, it likely will not replace traditional phone services because it relies on connecting to a user's existing phone via call-back to the called party. Another drawback is that Google Voice does not yet allow incoming number portability, so users will need to get a phone number assigned from Google. Google will allow outgoing number portability so users can take their Google Voice number with them to another provider.

So while Google is not an immediate threat to replace other VoIP service providers because it uses voice over the Internet and has robust calling features, as it scales up to a larger customer base Google Voice may become threatening to voice services offered by Vonage, Skype and magicJack -- leaving these VoIP-only companies more vulnerable than the telcos or cable companies that also own the "last mile" access.

Steve Taylor is president of Distributed Networking Associates and publisher/editor-in-chief of Webtorials. Larry Hettick is a principal analyst at Current Analysis.