Bypass the SP lock

The service provider (SP) lock is used to lock the cell phone to the SP's SIM card. Once the cell phone is locked to a specific operator, if one inserts a SIM card from a different operator the phone will refuse to accept it! The cell phone will however accept another SIM card from the same operator.

With a Nokia 16xx/21xx/31xx/ 51xx/81xx that are SIMlocked to one provide you can bypass the SP lock like this:
1: Insert sim card of different provider.
2: Turn on the phone and press the UP VOLUME key for 3 sec. then release it and the phone says PIN CODE?
3: Press the "C" key.
4: Then Press * and wait until it disappear and appear again, then press * one more time and 04*PIN*PIN*PIN#
the phone now says: PIN CODE CHANGED (or ACCEPTED) and the SIM card is accepted until you restart the phone again.
NOTE: On version 5.04 Nokia has removed this option!
Your number in your display
1. Go to menu 3-7 Call cost settings.
2. Turn ON the Call costs' limit 3-7-1. PIN2 code Required.
3. Put in the limit with the phone number. eg. my phone # is 019 2184697 Enter the limit as 2184697
4. Go to menu 3-7-2 Show costs in. PIN2 code Required.
5. Select Currency.
6. Enter Unit price: 1
7. Enter Currency name as 019 (per my phone # eg. above)now the phone number 019 2184697 will remains on the 4th row of the display.
Secondly, if you press the # key, it prompts which line to be used; Line 1 or 2.