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.
Shop for accessories specifically compatible with the Motorola i415.