Important codes for nokia mobile phones:

1) *#92702689# (to remember *#WAR0ANTY#)
This Displays:
   >Serial Number
   >Date Made
   >Purchase Date
   >Date of last repair (0000 for no repairs)
   >Transfer User Data (depends upon model)

2) *#7760# for Manufactures code.

3) *#06# for IMEI(International Mobile Equipment Identity) number.

Note: Most of the sites provide several codes which actually never works. They are just meant to fool you or increase post's popularity.