Using the range of services bundled with Google Voice was previously contingent on getting a "Google Voice" number -- a new phone number. Now Google will enable people to use Google Voice services, albeit in a "lite" version with slightly less functionality, with their existing mobile phone numbers. The Google Voice Blog explains:

Previously, when you created a Google Voice account, we asked you to select a new Google phone number. This allowed us to offer features like call forwarding, screening, and recording.  But we know not everyone wants to start using a new phone number, so we've been working on another option for people who are willing to trade some features for the ability to keep their existing number.

We're excited to announce that you now can get Google Voice with a Google number OR with your existing mobile phone number. If you choose to use Google Voice with your existing number, you won't get some features (like call screening and recording), but you'll still get many others -- including Google voicemail

Here's the distinction between the two levels of service:

if you sign up for Google Voice with your existing number, you'll get:

• Online, searchable voicemail
• Free automated voicemail transcription
• Custom voicemail greetings for different callers
• Email and SMS notifications
• Low-priced international calling

If you decide to also get a new Google number, you'll get all of the above PLUS:

• One number that reaches you on all your phones
• SMS via email
• Call screening
• Listen In
• Call recording
• Conference calling
• Call blocking

The skeptic or cynic might say this is a response to slow or slowing adoption and an attempt to push the service to more users, many or most of whom may not want to get a new phone number. Regardless the features and the "lite" service are quite useful. 

The existing number service will allow you to bypass your carrier voicemail and use the Google Voice features, which I'm going to do provided I don't get charged for call forwarding by Sprint (a question to investigate).  

It's also interesting to note, separately, that Google is using Voice to generate call-tracking numbers for its new local business ad product: Local Listing Ads. So the company will probably find a range of uses for the service.