Samsung is supposed to update their World's Smallest MP3 Player YP-T5 with the new model YP-ST5.
The Samsung YP-ST5 has increased battery power. The new world's smallest MP3 Player can play for 20hours. The YP-T5 only supports 8 hours of play time. The YP-ST5 features USB 2.0. In August a Firmware update should enable the YP-ST5 to support OGG.
I do not know where Samsung's claim comes from to call the YP-T5 the world's smallest MP3 Player. The coin-sized EMP-Z from EraTeach only measures 42mmx10mm. The YP-T5 measures 54x23x23mm. Oh well, makes a great headline though.
Info from posting at MPMate (korean).
The Samsung YP-T5 (256MB) currently sells for about $129.