The rumors were true: Republic Wireless today threw their disruptive hat into the mobile carrier game, launching their hybrid cellular/Wi-Fi service with a $19/monthly unlimited plan in the United States. Officially the service is a Beta, but Republic is open for business all the same. $199+tax up front gets you an LG Optimus S Android phone (the device supported at launch), and unlimited voice, text and data with no commitments or contracts. The service is advertised to work throughout the U.S., and also support calling from around the world to the U.S. via Wi-Fi (calling from the U.S. out to the rest of the planet isn’t yet supported). Your first month is included with the price of the phone, and service will run $19/month (plus tax) after that. There is a “catch,” of course, and Republic’s self-styled renegade disruptor image goes so far as to include a, “What’s the Catch?” link on their site that explains the fine print.

The Catch is basically this: Republic’s model is dependent on the majority of their customers using Wi-Fi, not cellular, connections the majority of the time. Rely on cellular (Sprint’s CDMA network) too much and you’ll be warned that your “Cellular Usage Index” is too high. Keep relying on cellular and you’ll get the boot:

So, over time, if you don’t bring your CUI back into a reasonable range, we’ll help you find a more suitable, traditional cellular carrier.

Okay, so how much is too much? What does Republic consider to be a reasonable range of cellular usage?

Even assuming 0% wifi usage, for example, you could consume 550 minutes, send 150 texts, and download 300 megabytes of data without crossing the community’s fair use threshold.

At first blush that might not sound like enough connectivity, but remember that’s “assuming 0% wifi usage.” If you’re connected to Wi-Fi most of the time, that might actually be plenty to get by. Imagine your phone is always connected to Wi-Fi at home and at the office – that takes care of weekday mornings, afternoons and some evenings. So you’re looking at some evenings, and some of the time on weekends – you know, when you’re “out.” Even at those times you might wind up at a friend’s house or in a cafe or bar with open Wi-Fi. Depending on your usage patterns, 150 texts and 300 MB for cellular-only situations might just go a long way each month.

Sounds like an interesting model that’s totally worth checking out if you can live with Optimus S as your phone. Republic’s Hybrid technology is baked into the device, so there’s no option for bringing your own handset to the party, though the company is talking a good game about expanding their hardware offerings:

The ultimate in smartphone freedom would be using the phone you want, on the network you want, whenever you want. We agree… and are working toward that ideal. For now, Big Cell makes the rules. Android phones, Wi-Fi and the Web fuel our optimism that the future could look very different.

Currently Republic is offering a 30-Day money back guarantee. I might have to sign up just to see how it works and find out how much cellular data I actually use (I’m one of those folks who’s Wi-Fi connected far more often than not). $19/month is roughly a 75% savings over what I pay now. Over the course of a year, we’re talking about $700+ in savings. Assuming the service works satisfactorily, would that be enough dough to get me to give up my iPhone 4? Interesting question. If Republic can offer a top-shelf Windows Phone device alongside of that Optimus S, my answer might just be, “Yes.”

What about you? Any of you game to give Hybrid Calling a shot?