Few days ago I sent a message on twitter "Anyone know the reason for Nokia's SIM Card Registration Failed problem?". Got quite a few solutions from my friends . It is the most common problem with Nokia mobile phones. Restarting the phone few times or removing SIM and cleaning the contacts also fixes the problem. Try some of the solutions that worked for me.
Solution 1: Blocked SIM or Faulty SIM
In countries like India, you need to register your SIM card. The cell phone company blocks the SIM if they don't receive the application within few weeks of activating the phone. Please check if this is case.
Take out the SIM and test it with a different phone, if the phone fails to read the SIM, get the SIM replaced. Few days ago this worked for a friend with a brand new Nokia handset here in Hanoi, Vietnam.
Solution 2: Clean SIM Contact Pins
Take out the battery and SIM card. Use a clean eraser to wipe the gold contacts of the phone and on back the SIM card. Replace the SIM and make sure its firmly held in place. Few phones tend to start to working when you bang them on your palm a few times due to this reason. Tighten the tiny screws on the back panel of the phone near the SIM card if they are loose.
Solution 3: Phone Software/Hardware Issues
Despite all your efforts, the phone refuses to work then try to the phone repaired or replaced. Some users found that the cellphone firmware upgrade tends to fix this issue. I got a Nokia phone firmware upgraded, it fixed the problem for few months. But the phone started to have the problem again.
Unfortunately there seems to be no sure fix for this problem. Most cell phone service centers including Nokia Authorized shops often fails fix this annoyance. They even charge you service fee just for checking the phone :( .