The Japanese carrier KDDI has just announced the Sony Ericsson Walkman Xmini phone to be realeased in Japan at the end of December. It measures 44 x 75 x 18mm (when closed) and features a 1.8-inch LCD display with 4GB of built-in memory. The Xmini can hold up to 2,300 songs from EZ “Chaku Uta Full”, KDDI’s mobile music download service.

When it’s closed, it looks like a regular Walkman music player and music controls appear under the display screen. When you slide it open, an alphanumeric keypad is revealed to give you normal cell phone capabilities. There is no information yet on whether the phone will be available in other countries.