Popular Mechanics just commissioned a test of cell phones under extemely low temperatures. As expected, the battery was usually the first to go:
[http://www.popularmechanics.com/technology/how_to/4337496.html|Does Cold Weather Injure Cell Phones? Abusive Lab Test]
They hit battery problems at -10F short-term exposure. I'm sure that they'd see the same degradation at slightly higher temperatures with longer exposure times.
It's clear that electronics don't handle extreme temperatures. It seems best to keep cell phones in your pocket so '''you''' keep it warm, and computers in warm cars or indoors.