The manual for the i415 says that in order to receive over-the-air Radio Service Software (OARSS) Security you must enable security the first time you power on the phone or within 10 days of first activation of your phone.
Is this necessary? I only use the phone for tracking.
It makes it easier for Boot Mobile to push the new phone firmware to your phone. If you don't have it enabled, then you'll have to manually upgrade the firmware with a USB cable when necessary.