Wirelessly posted (Mozilla/5.0 (iPhone; CPU iPhone OS 5_1 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9B176 Safari/7534.48.3) Yesterday I forgot to charge and the battery of my iPhone 4 was below 10% when I started my day. As an emergency measure I cut data off and switched to 2g network. Astonishingly, after one day of work and a good deal of calls, I still had juice when I got back home. I would be happy if Apple could offer as an option the automatic swich to a feature phone below say 5%. I guess that with some optimization of the os functions this "last drops mode" could allow for a full day of (crippled, of course) use away from a power plug.