Good find, Ogri..... couple of comments:
1. If you're in questionable coverage, its worth powering your phone off/on (or restarting the network select if you know how to do that). This restarts the algorithm that finds the best cell to call from. It shouldnt be needed, but sometimes the networks are quite setup as they should be
2. A voice call is always best, but if your coverage is poor an SMS has more chance of getting through, so register for that emergency SMS service. SMS certainly doesnt use different frequencies though
3. 999 also works in the uk (some older phones may even not have 112 hard coded as an emergency call).
4. Most phones will also make an emergency call without a SIM.
5. technology is wonderful, but I like to back it up by mundane things like letting people know roughly where i am and when I should be back.