This could be old news, but just to be sure...

PalmSource has announced at its developer seminar, currently under way in Munich, that Palm OS 6, code-named Sahara, will be complete by December 29th. The new version will focus on wireless technology standards, security and multimedia.
http://www.palminfocenter.com/view_story.asp?ID=5992


According to news out of the European Developer conference, PalmSource plans to continue to develop Palm OS 5, even after OS 6 is finished. The company will release a special version of OS 5 that will target mobile phones.
http://www.palminfocenter.com/view_story.asp?ID=6008

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Looks like we may see new versions of the T600 coming out sooner than we think!