Although some argued that the HTC HD2 was at the threshold in terms of size which could still be considered mobile, we've been seeing a decent amount of manufacturers
take it to the next level by offering displays that start at 5 inches. Sony Ericsson is looking into getting themselves situated with their own monster sized Android device which also looks to pack a hinged slide-out landscape QWERTY keyboard. There was an image taken that's alleged to be a Sony Ericsson smartphone donning a 5.5” touchscreen and Android 2.1. Currently it's rumored that this prototype unit is still in the early stages of testing, but there is no information whether or not Sony Ericsson plans on putting Android 2.2 on this behemoth of a smartphone. We've seen the company convert their Sony Ericsson Xperia X10 to smaller sizes, but this time around it's quite apparent that they're thinking on a larger scale.
source: IT168 Sony Ericsson BBS
(translated) via Engadget