Dropping its radios for cell service and turning itself into a tablet... The 6.4-inch Xperia Z Ultra may be big enough to pull it off, but are you willing to pay just under $500 (52,000 yen) for the pleasure? Sony hopes you will. It's a Japan-only deal for now (neatly tying in with KDDI's own 4G-capable Z Ultra, also announced today), but we could imagine it filling tablets shelves at your nearest electronics store. If Sony tells us anything more, we'll let you know.