SIM-unlock: * # 7 4 6 0 2 5 6 2 5 # is supposed to SIM-unlock the 8110 and the 1610. However, I have heard that some manufacturers base the SIM-unlock code on the actual IMEI (serial Number) of the phone itself, and this code may work only one one specific phone.
Results obtained so far:
One person in Finland reports that entering this code in an 8110 with firmware version 4.36 results in the message "SIM CLOCK STOP NOT ALLOWED". I have no idea what this means.
Nokia 8110 FAQ