I love my iphone, and I honestly can't remember how I managed the first 60 years of my life without it.

However, I have learned they don't like the cold very well. When cross country skiing around town, I usually carry mine in a pocket in one of my inner layers, so it stays toasty warm. However the other day, without thinking much about it I put it in an outer pocket. Temperatures were somewhere around 0 to 5 F (minus 18 to minus 15 C). We were getting near a friends house, so I pulled it out to call and see if he was home.....and my iphone was dead. I wasn't too surprised, since in general, most battery powered items don't like the cold. After getting indoors and letting it warm up, it worked fine. However, it did motivate me to doing a bit of web searching. Turns out, Apple's published iphone specs are:

Operating temperature: 32° to 95° F (0° to 35° C)
Nonoperating temperature: -4° to 113° F (-20° to 45° C)

I'm sure those are pretty conservative numbers, but at least in theory if you exceed those ranges it could void your warrenty.

Even more disturbing, there have been reports on the web of iphones whose face plate shattered when left out in serious cold (overnight in a parked car for example).

Like I said, I love my iphone, but I will take care to keep it warm!