Google has just released a mobile version of Google Voice for Android and BlackBerry phones. Still in an invite-only beta stage, the free service lets users combine work, home, mobile and any other phone under a single number (provided by the search giant) for all of their incoming and outgoing communications. The new app lets you make or receive calls using this number, integrates with your phone’s contacts, and provides access to the service’s visual voicemail and voice transcription features.

One particular element the company is touting with the service is the ability to make international calls through your local Google Voice number at a reduced rate – starting at $0.02 – instead of those from your wireless carrier. It also allows for text messages to be sent and received for free through your Google number, again bypassing the carrier.

You still need your phone service to place calls using Google Voice, since calls are not going over the data connection or Wi-Fi; but carriers may not be so pleased with this service nevertheless. Users with Friends & Family calling plans, for example, could simply add their Google Voice number to the list and theoretically get unlimited outbound and inbound calls to any number without the hassle of actually paying for it.

In addition to the applications for Android and BlackBerry platforms, Google also says a version is in development for the iPhone. But will Apple and AT&T let Google ship such an app without limiting it?