I have featured linux on mobile phones several times already so it won't hurt to feature another one. :)
Trolltech releases the Qtopia Greenphone, "a Linux mobile development device open for unlimited software innovation. Greenphone offers a development environment that is equivalent to a GSM/GPRS mobile phone with the capability to re-flash the applications memory."
So what does it mean to have a development environment? Well, LinuxLookup provides a brief review of the Greenphone. Whilst the Community SDK is completely free, the device costs a whooping USD695. I wonder if they provide an emulator. :)