I haven't been kind to Garmin, mostly because Garmin hasn't been kind to its users. It's a heavy battery hog with a kludgy interface that I have been eager to replace. Most of my posts since late October have been about how to punt on Garmin.
And from every indication, you can do that most everywhere for at least three seasons.
But there could be cause for caution: temperature and altitude extremes.
According to Apple's web site, the environmental requirements for my iPhone 4s are: 32 to 95 degrees F and a maximum altitude of 10,000 feet.
Garmin says my Oregon 450t has a range of -4 to 158 degrees F and no altitude limit.
I've not been able to get anyone from Apple to respond to my questions about whether their limits are based in reality or in some sort of CYA logic.
I do know that last August when I took both my Garmin and iPhone on the 14,042-foot summit of Mt. Langley, the iPhone performed identically to the Garmin.
However, temperatures didn't get much below 32F judging by the scarcity of ice in still water.
I'll take both the iPhone and Garmin along with a thermometer at the end of December when I take a three-day winter mountaineering course that will summit the 12,279' California Matterhorn in the Eastern Sierra.