Frega originally purchased the machine from someone on Craigslist for parts for his repair business. After opening it Frega noticed that (in addition to the integrated antenna) also had a red logic board. Apple's production boards are typically either blue or green, so this sent up an immediate "red flag."
It's essentially a 2007 MacBook Pro with a retractable antenna around the monitor bezel, a SIM card slot, and matching 3G hardware.
Frega had a friend post the ultra-rare Mac on eBay where it was bid up to $70,000 in a little less than a day before being removed at the request of Apple who cited copyright and intellectual property infringement.
There's that, and the fact that the prototype is practically identical to an Apple patent filed in 2008.
Lowensohn reports that Frega said he was contacted by Apple this afternoon "to have someone from the company pick it up."
Check out this ZDNet photo gallery of the ultra-rare 3G MacBook Pro.