Enter special code
If this happens, turn off your phone. Put the Boost Mobile SIM card back in the phone. Turn the phone on and let it sit for 15-20 minutes. The display will change from Wait ... to Enter Special Code ______. Turn the phone off one more time, and turn it right back on. Your phone should boot normally.
I found this out by accident when trying to see if a NexTel SIM card would work in the phone. Boost Mobile customer service couldn't help, and Motorola customer service was offering to repair the phone under warranty.
This was much easier.