If you want to see what's next for Android in "Cupcake"—including that delicious on-screen keypad, you can grab the SDK and root around yourself before T-Mo pushes it to your G1.
We've known how this Cupcake tastes for a few days now, and we're still most excited about the soft keypad, of course, which will come in handy in the many situations where you don't want to flip open the G1 just to type a few letters. There are also a few mysterious new apps, some of which look like dev tools but may be polished for eventual release, as well as hints of haptic feedback for the keyboard and a few more tidbits.
If you want to load Cupcake on your computer via the Android SDK, grab the SDK here. Then, follow the instructions laid out by the folks at Nullwire (very easy) to replace your system image files with the new 1.5 Cupcake versions, then simply run the "emulator" app (a UNIX executable on OS X and Linux, and an .exe in Windows) inside the SDK's "tools" directory and you're in business. [Nullwire]