At your advice, I reset the device through the manual steps (with the volume down button and the power on button). Now, after powering the unit "On", the phone will show the LG screen for 7 1/2 minutes, then show the T-Mobile splash screen for 1 1/2 minutes, and then show the T-Mobile splash screen again and again every 26 seconds. Now, there is no way to get to the Home screen anymore. The only way I can turn off the phone is to re-seat the battery.
-deerleg