Waterproof & Numb hands
Easy to make a phone waterproof. Go a marine chandlers and you can buy a sealable PVC envelope. Better still you can still hear through it. Modern phone with flip-open style or slider won't work too well with this though. This phone would work ok with the PVC envelope as it is a simple keypad job. Might even survive a moderate dive in the PVC sleeve.
If you can't work this in anything other than light gloves then it won't work well for you when you hands are truly numb, as in winter watersports ! Pay attention to the number you are dialling ! Bet you get it wrong first time due to clumsiness. However I commend the strong case and design - more of these designs required. I hope it works in the environment intended.
GPS on this would be good, especially as it is most likely to be used by hillwalkers and climbers. Position fix would be good. 'Oh shit accident, location blah blah, please help'.
If the phone survives a severe impact, where you are really badly hurt, but it enables you to call for help, then it has done it's job.