[aatreya]

I have this problem too - exactly as you describe.
It's REALLY annoying!

My understanding of it is that when the radio gets some sort of update, like an incoming data packet or a switch to 1x data from EVDO, it sends an interrupt to the main chip to let it know what happened. However, some idiot engineer didn't bother to process these properly to keep the phone off when it happens, so the damn thing turns on randomly. Sprint needs to get their crap together and fix the radio stack, so this doesn't happen all the time.

I've considered writing a program that will immediately turn the phone back off if the user didn't explicitly push the power button, but I'm not sure if this is possible.