According to a post on PalmAddict, PalmSource has decided to shift development efforts from Cobalt (PalmOS 6) to focus on a Linux-based version of its PalmOS software and intends to release a Linux-based mobile phone, probably in 2006.
This radical change is likely a result of the purchase of China MobileSoft, a company whose expertise lies in Linux-based phones.
Development on Cobalt and other projects will apparently be delayed. It could be that we will never see new Cobalt-based devices.
Source: Pocket PC Thoughts