When I got up this morning the temperature outside was about -20°C (-4°F). That's nothing though, as about 200km from here they measured a country-low -37.2°C (-35°F). Whenever I'm outside, I make sure that my phone is deep in my pocket in order to actually have a phone when I get back inside. I'm not just paranoid, and a new test done by the Finnish magazine mikroPC (in a controlled weather chamber) shows exactly how far gone cellphones can end up if used out in the cold.
The chart shows when the phones started showing issues (like SIM card errors) and when they gave up and turned themselves off. The iPhone 4S and Nokia N9 both started showing problems at only -5°C (23°F), but most phones lasted until -20C (-4°F) before actually turning off. The iPhone 4S only lasted until -10C before turning off though, being the first one in the test to do so. Samsung's S II and Xcover phones were the two proper smartphones that lasted the longest, giving up at -35°C (-31°F). A few dumbphones lasted the absolute longest though, which makes sense – less going on under the hood.
Among the issues experiences before total shutdown were LCD update issues (where AMOLED phones lasted longer), power issues (cold weather reduces battery power drastically), touch input issues and so on. As far as liability goes, manufacturers are pretty "clever" with marking products with operating temperatures that don't really fit some parts of the world all that well. We have pretty strict (for the companies) consumer laws over here, and I'm surprised that this has been able to slip under the radar. If you sell a portable device in a cold country, they should be able to take it.
While this doesn't mean that phones will instantly turn off at X degrees as soon as you take them out of your pocket, it does go to show exactly how fragile some devices are. Here in Norway there have been cases of iPhones that have shattered from the cold, which is yet another nail in the coffin for glass back plates. I myself had serious issues with a Sansa Fuze a few years back, as it didn't survive my hour long dog walks in -15-20°C even if it was in my pocket.