No, you can't have a Today Screen on the G1 Phone (yet). An equivalent screen on the G1 is the Home Screen, and unfortunately developers can't create "widgets" (like the clock) as of yet. Once Google allows developers to create widgets, I'm sure you'll see some cool Home Screens.
Being a Pocket PC and Windows Mobile application developer for the last 7 years, I know a lot of things the WM devices can't do that the G1 can do very easily.
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