According to the updated Phoenix FAQ, Blake Ross will soon be working on a standalone mail client called Thunderbird. Mozillazine says Thunderbird is simply Minotaur renamed. They are targetting a Thunderbird 0.1 release around the same time as Phoenix 0.5. There’s currently no scheduled release date for Phoenix 0.5, but based on comments that 0.4 will leverage the Mozilla trunk freeze for 1.2 scheduled for a release November 8, we can guess that we’ll see something in November. Blake posted more details about his plans.
I notice that the Phoenix 0.3 release is going to slip a week to around October 14 due to the 1.2beta.