Bypass the SP-lock

With a Nokia 16xx/21xx/31xx/51xx/81xx that are SIM locked to one provider you can bypass the SP lock like this-

Insert sim card of different provider.

Turn on the phone and press the UP VOLUME key for 3 sec. then release it and the phone says PIN CODE 

Press the "C" key.

Then Press * and wait until it desapear 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.