It's time to return my Acer Liquid review unit. The crucial step to do is 'wipe' all personal data from the device. However, Acer Liquid comes with Android 1.6, which does not have 'wipe' option in Settings. You need to do 'factory reset' from hidden boot sequence instead.
Here is the solution from Acer Liquid manual:
Press and hold the Power until you feel your smartphone vibrate and/or you see the Acer logo screen. Press and hold the Volume up and Volume down buttons.
When you see the 'clean boot' screen, please volume up/down to change value and press camera button for confirmation.