*3001#12345#* + tap Call. Enter Field Mode. Field mode contains lots of iPhone internal settings, especially newest network and cell information.
*#06# It shows your IMEI number. IMEI number is a unique identification number for your mobile phone hardware.
*777# + tap Call. It shows account balance for prepaid iPhone.
*225# + tap Call. It shows 'Bill Balance' for Postpaid only.
*646# + tap Call. Using this you can check remaining minutes (Postpaid only).
*#21# + tap Call. It is used to set interrogation for call forwards. It discover the settings for your call forwarding. Using this you can check whether you have voice, data, fax, SMS,sync, async, packet access, and pad access call forwarding enabled or disabled on your iPhone.
*#30# + tap Call. It is used for check the calling line presentation. This shows whether you have enabled or disabled the presentation of the calling line, presumably the number of the party placing the call.
*#76# + tap Call. It is used to check whether the connected line presentation is enabled or not.
*#43# + tap Call. It is used to check if call waiting is enabled for your iPhone or not. It also shows call waiting status for voice, data, fax, SMS, sync data, async data, packet access and pad access. Each item is either enabled or disabled.
*#61# + tap Call. Used to check the number for unanswered calls. It also show the number for voice call forwarding when a call is unanswered and also show the options for data, fax, SMS, sync, async, packet access and pad access.
*#62# + tap Call.  This code can be used to check the number for call forwarding if no service is available.
*#67# + tap Call. This code can be used to check the number for call forwarding when your iPhone is busy on another call.

* # 33 # and tap Call. Check the service call to the call-barring (enabled / disabled)

Restoring Original Settings, and Removing Old Pass code

1. • 1 Connect your USB cable to your iPhone and your computer.
   • 2 Turn off your iPhone by pushing the power button on the top of the phone and waiting for a slider to appear on the screen. Then, slide the on-screen slider as directed when it appears on your iPhone.
     
      
   • 3 Turn your iPhone on by simultaneously holding down the power button and the home button. The home button is the circular button in the middle of the lower portion of your iPhone face. A yellow sign indicating you are in restore mode will appear on the iPhone.
   • 4 Start the iTunes program on your computer by clicking on the icon on your computer screen or by selecting it from the Start menu.
   • 5 Click on the summary tab when iTunes starts. The tab is at the top of the screen.
   • 6 Click on the "Restore" button. This restores all the original settings on the iPhone.

   Setting New Pass code

   • 7 Select the settings icon on your iPhone.
   • 8 Click on the option for general settings, and then the option for the pass code lock.
   • 9 Enter a four-digit code that will be used in the future to unlock your iPhone. Others cannot use your iPhone without the code. Your iPhone will require you to enter the four-digit code a second time to confirm and set the code.
   • 10 Select how often you want your iPhone to require the pass code to be entered.