Mobile phone locked OR Not able to unlock mobile phone

When you place a new or a existing SIM card from another phone provider into a different cell phone, it asks for a Security Code and you don't have it with you. This means that a mobile phone is locked to the original mobile phone provider.

You need to contact this mobile provider to ask for the unlock code (Security Code) for this phone.
For this you need to provide proof of ownership etc.

Following are the possible action items you may do, when you come aross the above situation:

1) Get security code/restriction code to unlock the cell phone from the current cell phone service provider.

2) If your phone provider does not help you then this WEB site it provides security codes for a small price.
http://www.mobileunlockstore.com/?gclid=CKDb2_y2558CFSlJagodxBkDHw

3) Try this WEB site also - UnlockFree http://www.unlock-free.com

4) You can also try this WEB site : http://www.mobileunlockguide.com/mobile-phone/

5) For Nokia phone - try this WEB site too : www.unlock-free.com/nokia-master

6)The IMEI number is unique for each mobile phone. The number is printed on the label under the battery.
You can also get the IMEI number by entering this on your phone
*#06# It will then display your IMEI number and you may also get a unique global serial number. Your IMEI number should be 15 digits.

Also read post on PUK information

Personal Unblocking Code (PUC / PUK)

A PIN Unlock Code (PUC) or PIN Unlock Key (PUK) is used in GSM mobile phones and some smartcards to unblock a blocked card.

Most mobile telephones offer the feature of personal identification number (PIN) protection. After switching on the phone, if the PIN security function is active, the user is requested to enter a 4-8 digit PIN enabling the phone's non-emergency calling functions.

If the wrong PIN is typed in more than 3 times, either the SIM card, the device or both become locked. They can be reverted to their original unlocked state by entering a PUC (PUK), provided by the service operator through verification.

If the wrong PUC (PUK) is entered 10 times in a row, the device will become permanently blocked and unrecoverable, requiring a new SIM card. Cellular phone users are therefore advised by most providers to keep their PUC (PUK) written down in a safe place separate from the device.

The PUC (PUK) is a SIM-specific code assigned by the service provider. It is near-impossible to guess and enter it; thus, if you do not know your PUC (PUK) and are prompted for it, you should get it from your service provider.

Please note (for Indian customers): You may directly contact the service provider and get the PUK number. For this you just need to have the mobile number.

Also read post on mobile phone locked/ forgot phone unlocking password