Using phones as wallets is plain stupid
The keys are not stored on the phone alone. It stores the key on a microSD smart card. (Actually, it uses a split key system, which requires both the phone and the SD card to recover the key-- which is even safer-- you can read about it here:
http://www.othercoin.com/OtherCoin.pdf )
It's just retarded, there is no need to speculate or explain anything, the very concept is extremely stupid on a fundamental level. Should every person on earth who wants to use crypto in person also have a phone? Do you know how long the battery lasts for modern phones?
In the future there will be small plastic computers the width of a paper bill that you would swipe against each other in order to pay, they will be so cheap to manufacture that you could simply swipe your reserves to a new bill instead of recharging, they would also be so efficient that you would be able to recharge them by manual means.