The Emergency Number worldwide for Mobile phones is 112, not 911. If you find yourself out of the coverage area of your mobile network and there is an emergency, dial 112 and the mobile will search any existing network to establish the emergency number for you, and interestingly 112 can be dialed even if your keypad is locked. Try it out.
Have you locked your keys in the car, again? Does your car have remote keyless entry? This may come in handy someday. If you lock your keys in the car and the spare keys are at home, call someone at home on their cell phone from your cell phone. Hold your cell phone about a foot from your car door and have the person at your home press the unlock button, holding it near the mobile phone on their end. The door will unlock. Saves someone from having to drive your keys to you. Distance is no object. You could be hundreds of miles away, and if you can reach someone who has the other 'remote' for your car, you can unlock the doors (or the trunk). This is like the old phone dialer trick. HOLLA!
My cell battery is always low. But if you dial *3370# your cell will restart with a reserve and will show a 50% increase in battery. This reserve will get recharged when you charge your cell next time.
And this last one is the best tip I've got for that ass: Cell phone companies charge $1.00 to $1.75 or more for 411 calls when they don't have to. When you need to use the 411 information option, simply dial: (800) FREE 411, or (800) 373-3411 without incurring any charge at all.