Here are some more codes for Nokia

#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)

*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)