The iPhone 4S is not exactly a 4G phone, even though AT&T makes you think it is. However, here is an accessory that delivers 4G love in WiMAX flavor to the iPhone 4S and iPhone 4. It is called the Freedom Sleeve 4G and is basically consisted of a 4G WiMAX radio and a Wi-Fi module enclosed within a protective case along with a battery.
Once the iPhone is outfitted with the accessory, it automatically connects to the Sleeve's Wi-Fi network. And you know what is really cool about the Freedom Sleeve 4G? That the WiMAX wireless broadband that you get is free of charge! Up to 1GB can be used for free and shared with up to 8 other Wi-Fi devices.
You cannot get one of these yet, but a limited number of Freedom Sleeve 4G cases are available for pre-order. Priced at $99, they are available at the company's web site, so just follow the source link if you are interested. The video embedded below shows off the accessory in action.