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

Nokia Mobile Phone Unlock & Hidden Feature codes

These codes will work on most Nokia Mobile Phones to activate/deactivate advanced hidden functions that you can’t change through the phone menu

One useful function that all Nokia’s I’ve owned have is “Cell Info Display” which can usually be found in the phones “Display settings” (eg: in a Nokia 1600) or “Phone Settings” (eg: in a Nokia 3315)

If your network supports it, when “Cell Info Display” is enabled, it will display the name of the base station your mobile is currently connected to on the screen eg: when i’m walking around the city it says “Sydney CBD” and when i’m at home it displays the name of my suburb.

Note:

To display “p” press “*” three times within one second, To display “w” press “*” four times within one second, To display “+” press twice “*” within less than a second

Code Function

*3370# / #3370# Activate / Deactivate Enhanced Full Rate Codec (EFR) – Your phone uses the best sound quality but talk time is reduced my approx. 5%

*#4720# / *#4720# Activate / Deactivate Half Rate Codec – Your phone uses a lower quality sound but you should gain approx 30% more Talk Time

*#7220# / *#7230# Enable / Disable PCCCPH support (faster GPRS)

#pw+1234567890+1# Provider Lock Status. (use the “*” button to obtain the “p,w” and “+” symbols)

#pw+1234567890+2# Network Lock Status. (use the “*” button to obtain the “p,w” and “+” symbols)

#pw+1234567890+3# Country Lock Status. (use the “*” button to obtain the “p,w” and “+” symbols)

#pw+1234567890+4# SIM Card Lock Status. (use the “*” button to obtain the “p,w” and “+” symbols)

12345 This is the default security code

*#0000# Displays your phones software version,  

1st Line : Software Version,  

2nd Line : Software Release Date, 

3rd Line : Compression Type

*#9999# Phones software version if *#0000# does not work

*#06# For checking the International Mobile Equipment Identity (IMEI Number)

*#67705646# Removes operator logo on 3310 - 3330

*#73# Reset phone timers and game scores

*#746025625# Displays the SIM Clock status, if your phone supports this power saving feature “SIM Clock Stop Allowed”, it means you will get the best standby time possible press and hold # Lets you switch between lines

*#7760# Manufacturers code

*#7780# Restore factory settings

*#8110# Software version for the nokia 8110

*#92702689# Displays – 1.Serial Number, 2.Date Made, 3.Purchase Date, 

4.Date of last repair (0000 for no repairs), 

5.Transfer User Data. 
To exit this mode you need to switch your phone off then on again

Source