Apparently, the radiation emitted by a mobile phone (depending of course where it is located in the aircraft) can cause the outflow valve to open on the B737... The pressurization controller isn't very well shielded from electromagnetic radiation...
Read some articles about research done on this subject. Seem to remember that they DID find that mobiles can cause severe interference to aircraft systems, but they had trouble to reproduce the effects. Location apparently has a great influence; 30cm more left/right could change the effects completely.