This is a very old news, but I think if is interesting to people willing to use G1 to update its kernel and Android file system completely.
Let me explain: Google/T-Mobile sold G1 phone completely locked. Then people discovered how to unlock the filesystem (“root” it), but anyone could compile Android system (kernel + rootfs) and flash it into phone. Then Google decided to create a ADP1 phone for people willing to develop Android firmware (instead just Android applications).
Hopefully some guys discovered how to remove security from its bootloader, then you can upload an unsigned firmware with no problem:
Note: Motorola released Droid on USA with bootloader unlocked to load unsigned firmware, but release Milestone (same Droid hardware) on Europe but with bootloader locked. I’m not sure about Cliq (USA) e DEXT (Latin America), but I think the same apply.