GSM, or Global System for Mobile Communications, is a network protocol used by cell phone service providers worldwide. The easiest way to tell if your cell is a GSM network phone is by removing its battery and checking to see if there's a SIM card underneath it. If there is, then you've got a GSM phone. By employing little tricks, you can enable or disable features.
Display IMEI Number
To obtain your phone's IMEI number, which comes in handy when remote unlocking your phone, type "*#06#" into your keypad, followed by the "OK/Send" key.
Call Forwarding
If you're on your cell phone and you don't want to respond to a call, defer it to your home or office phone. To activate call forwarding, type "*21*[your phone number]#", where "phone number" is the number where you want the call to be sent. To deactivate this, type "#21#".
Call Waiting
To disable call waiting, type "#43#" into your phone's keypad, followed by the "OK/Send" key. To enable it, type "*43#", followed by the "OK/Send" key. To check the status of your call waiting, type "*#43#" followed by the "OK/Send" key.
More Ring Time
To change the amount of time it takes for your phone to defer a call to voicemail, type "**61*[your voicemail number]**[number of seconds]" followed by the "OK/Send" key. "Number of seconds" represents the amount of time you want to allow before voicemail picks up.
Hide/Show Number
To hide your phone number from a person's caller ID, type "#30#" before dialing his number and then the "OK/Send" key. If you have options in your phone already set to block your phone number, type "*30#" before making a call to make your number appear.
Call Barring
To bar all calls, ingoing and outgoing, without a password, type "**331*[password]#" and then the "OK/Send" key. To deactivate call barring, type "#331*[password]#". "Password" represents the password that you've set to configure different things on your phone. If you don't remember setting a password, try "0000" as a default.
Tags: your phone, followed Send, phone number, your phone number, amount time, call waiting type