For the first 2 flashing jobs I got them from TOPSONY, downloads tab, and the latest flash I did on the phone I used SE upgrade service and I flashed in the latest firmware for K750i.
the next test I'll do is to take the phone in an area with no signal. There I can test of the network reboots my phone. And I'll probably decide if it is a HW problem like FLASH IC or processor or Radio AMP problem.