One of Sony-Ericsson's flagship Walkman phones has leaked online today through an auction. Selling from a Polish firm named Artkom, the K123i is reportedly a prototype of a future W-series slider nicknamed the Shinobu. Unique to the phone and its eventual production version is one of the first 16.7-million full color LCD in a Sony-Ericsson phone, say reports; it should also have HSDPA for 3G wireless and a front camera to match for video calls on supporting networks. A 2-megapixel camera will face the rear in the 0.49-inch thick device.

Artkom is auctioning the Shinobu for roughly $711 at the time of the original posting, though the official price is expected to reach closer to $580 by the actual debut. Availability is unknown but believed to include the US when the phone launches, which will likely be soon due to the near-production quality of the prototype. [via Esato forums]