The Sleeve fits over the iPhone 4 and 4S to replace the devices' standard 3G connectivity with FreedomPop's 4G service.

But the FCC has yet to approve one of its design elements, and so far, that delay has cost Freedom Pop $550,000.

As part of the design of FreedomPop's iPhone Sleeve, the WiMax radio sits right next to the iPhone's cellular radio, FreedomPop CEO Stephen Stokols said in an interview with Firece Wireless. But since the FCC has never tested a device with a "radio-against-radio" design," the agency had to do more extensive testing, therefore slowing down its approval process.