Disclaimer: These tips and tricks may or may not work with your mobile phone or carrier, use them at your own risk.

Cell phone specific tips, tricks and secrets:
LG    Motorola    Nokia    Samsung    Siemens-BenQ    Sony Ericsson

General tips and tricks:

Emergency
The emergency number worldwide for mobile phones is 112. 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. Interestingly, 112 can be dialed even if the keypad is locked. Try it out.

How to disable a stolen phone
First, check your mobile phone’s IMEI number by keying in: *#06#
A code will appear on the screen. This number is unique to your handset. Write it down and keep it somewhere safe. If your phone ever gets stolen, you can phone your service provider and give them this code. They will then be able to block your handset so even if your thief changes the SIM card, the phone will be totally useless. Most likely you will not get your phone back, but at least you will know that whoever stole it, can’t use or sell it. If everyone would do this, there would be no point in people stealing mobile phones.

Free 411 calls
Cell phone companies are charging us $1.00 to $1.75 or more for 411 information calls when they don’t have to. Most of us do not carry a telephone directory in our vehicle, which makes the situation even more of a problem. When you need to use 411 information option, simply dial:

1-800-FREE-411 or 1-800-373-3411 without incurring any charge at all.

Program this into your cell phone now. You may have to listen to a 10 second ad, but it is well worth it.

What is IMEI number or code?
IMEI stands for International Mobile Equipment Identity. IMEI is a unique 17 or 15 digit code used to identify an individual mobile station to a GSM or UMTS network. The IMEI number uniquely identifies a specific mobile phone being used on a mobile network. Using the IMEI, a phone can be blocked from the network quickly and easily. As mentioned earlier, swapping a SIM card will not stop a phone from being banned. IMEI numbers are stored in the phones themselves, not on the SIM cards.

Hidden battery power
Imagine your cell battery is very low. To activate the reserve power, press the keys *3370# and your cell will restart with this reserve and the instrument will show a 50% increase in battery. This reserve will get charged the next time you charge your cell phone.