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Though FreedomPop remains mysterious on exactly when its “free” mobile broadband service will go live, it seems to be nearing a launch date. The company started selling it’s first product online, a WiMAX sleeve that fits over the iPhone 4 and 4S(s aapl). FreedomPop also revealed a new wrinkle in its pricing – or lack thereof. Instead of the 1 GB of free monthly data it originally advertised, customers will only get a guaranteed 500 MB, though it is providing mechanisms to boost your monthly allotment of gratis megabytes.

Some of you may be crying foul right now, but in fairness to FreedomPop, it has never said every customer will get an automatic 1 GB bucket every month – at least not to us. In an interview with GigaOM in March, VP of marketing Tony Miller said FreedomPop aimed to give away a large block of free data each month, and while its target was 1 GB, it wasn’t set in stone. In addition, FreedomPop’s plan was to turn data into a digital currency, which customers could earn and trade. Customers could earn more megabytes by referring people to FreedomPop and by signing up for the carrier’s still unidentified value-added services. Also, customers who don’t use up their monthly data allotments can transfer their extra megabytes to friends.

The basic structure of its free data model is now starting to emerge. According to its Website, customers who order the iPhone sleeve will get 500 MB free each month, but it appears customers can increase the size of their free buckets to 1 GB a month, though FreedomPop isn’t saying how just yet. After customers use up their free buckets, they will be charged at a base rate of 1 cent per megabyte.

The Freedom Sleeve iPhone shell — which triples as a spare iPhone battery and a mobile hotspot — will tap into Clearwire’s(s clwr) WiMAX network so coverage will be limited to its 72-market footprint. While FreedomPop is taking pre-orders for the device online, it is also checking addresses to make sure you’re in a 4G market. That makes sense since FreedomPop doesn’t have a 3G — or any other — network to fall back on. You’re either in WiMAX coverage or you have no service.

The virtual operator is also scrapping the original deposit model it described. You buy the sleeve upfront for $99, though it seems that at any time you can return the sleeve in good condition for a refund, which amounts to the same thing. TechCrunch is reporting that FreedomPop is making the change for accounting reasons, allowing it to manage the device orders as revenue, not deposits.

When ordering the device, FreedomPop guarantees that you will receive your sleeve “before the rest of the world.” That’s not terribly helpful, and the wait could wind up being a few months. FreedomPop has said it would go live in the third quarter, which begins July 1, and in a press release issued Thursday it said would launch its beta service sometime this summer.