Activating the G1
From Android Wiki
Currently you can activate the G1 over WIFI without the need for a SIM Card.
For all ADP1 phones, simply do the following
1. Install the Android SDK
2. Run the following command from a terminal "adb -d shell"
3. From the shell prompt, issue the command "am start -a android.intent.action.MAIN -n com.android.settings/.Settings"
4. Turn WIFI on in the Settings of the Android Phone and select your wifi card
5. Exit the shell prompt on your computer and the Settings application on the Phone
6. Proceed with the activation
For anyone without an ADP1, follow the instructions at http://www.gotontheinter.net/content/faq-unlockingactivating-g1-or-adp1-without-sim-card.
Source(s): Android solutions