Google Voice is the next step in world domination from Google. It's a web-based service that lets you use one phone number for all your phones, and it's now available in the form of cellphone apps. The first two were just released yesterday — one for the BlackBerry, and the other for the Android operating system. Lucky enough to have been invited to use Google Voice, we picked up our T-Mobile G1 cellphone and fired up the Android app store (they call it "Market"), downloading the free Google Voice app in a matter of seconds.

Our first impression: It's excellent. If you use its text-messaging feature, none of your text messages will count against your carrier's text-messaging plan (never having to pay that price-gouging 10 cents apiece for text messages above your plan limit… priceless). That's because this uses the data portion of your connectivity to send SMS messages, and not that nickel-and-diming text messaging of T-Mobile.

And that's just the beginning. Hit the jump for more reasons to try Google Voice.

More coolness: Because the application routes your cellphone call through Google Voice, your GV phone number shows up to whomever you call. This will assist you in your migration to a single phone number for your cellphone and landline, because all of your calls will appear to be coming from that number. That's the number everyone will see, and they'll probably use it to call you back, getting them in the habit of using your new number.

The gee-whiz part of Google Voice is the way voicemail messages are converted into text and sent to you. On Android, there is a great karaoke-like application that shows you that converted text, where each word is highlighted as the audio portion of the voicemail message plays back to you. You can have that audio playing back either through the handset or over its external speaker.

First out of the gate are these two applications for BlackBerry and Android, but what we're really hoping for is an iPhone version of this mobile Google Voice application. There's no official word on when that might appear, but we're skeptical, thinking that AT&T might not want to let that text-messaging bonanza slip away.

Meanwhile, Google Voice spreads far and wide. Invitations are going out to a lot of people, so make sure you get your name on the list, and give it a try for yourself. So far, we like its Web-based implementation, the ability to screen calls and even listen in on someone leaving a voicemail message, and the convenience of having one phone number for our different telephones. It's a big leap forward in communications convenience, and so far, we haven't seen any drawbacks. That could change, so stay tuned.