That particular day was around 30ºF (-1ºC) but while testing and learning I have flown in temps as low as around 15ºF (-9ºC). When not flying, I keep iPhone and MP batteries inside my coat next to me. I have had no problems so far with either my Phone or the MP in those conditions. One time after burning through one battery, I started to fly on the second battery and at lift off I received a cold battery warning. I just let it hover at a couple of feet and watched the battery stats until it warmed up. I then continued to fly without any trouble.
I think -30 C could cause issues though, not only for your phone, but pushing the limits of the MP as well. My initial plan is to only fly on reasonable weather days. Definition of "reasonable" is still to be learned though.