There are a lot of speculations about upcoming release of the Samsung D900's successor - the Samsung D910.
The D900 featured a 3.13MPix camera, document viewer, TV-output
function, Bluetooth connectivity, expandable microSD memory, etc.
The new Samsung U600 doesn't differ much from its predecessor. It is
2mm thinner (10.9mm) than D900 which makes it one of the thinnest
sliders in the world. The phone supports quad-band GSM, GPRS, and EDGE
networks and features a 2.2" display, 3.2MP camera, expandable microSD,
60MB internal memory, multimedia player (MP3, AAC and WMA files), a web
browser, email client, etc. For now Samsung SGH-U600 is a great
replacement for the older D900 slider.