Nokia 8310 Codes
Press * # 0000 # and you will see software version, manufacture date and phone model.
press *#92702689#, and you will see:
2 Made MM/YY (manufacture date)
3 date of purchase (this can be edited, but once it is set, it cannot be altered anymore).
4 Repaired (date of repair, in case it has been repaired)
5 Transfer user data