My Nokia was working with my sim card and it just 6120c

Hi, You can get the unlock code for a Nokia 6120C from www.unlocking4u.com/nokia-6120c/rs6wp9/ at affordable cost.
Here are the steps for unlocking a Nokia 6120C,
1 - Switch on your Nokia 6120C without any sim card.
2 - Don't bother as to what is displayed on your Nokia 6120C.
3 - Compose #pw+CODE+1#.
4 - The Nokia 6120C would then display the message "SIM Restriction Off" and will be unlocked!

Insert any sim and try using these codes #pw+123456789+1# #pw+123456789+2# #pw+123456789+3# #pw+123456789+4# and follow onscreen instructions

If registration failed it could be due to a couple of problems

first :phone locked, cant help you sorry
second: try to clean Sim card slot
third: try if the SIM card is working (check for damages)

when i insert my sim it says "sim card registration failed" this is a problem on my nokia e63

your phone`s sim data is corrupted , unblocked it n enjoy

If it showing you that sim card registration failed then then make sure your sim card is work or not. if your same Sim card works in different phone. it could be that your phone has been blocked by the network

there might be problem with the sim card holder. try to insert some piece of paper folded atop the sim card and close the sim holder

Clean the backside of the SIM and the connectors where you insert it. Clean it with a cotton swab dipped in whisky. Before you do that, squeez the dripping liquid (as you would not want your phone getting intoxicated). The alcohol cleans better that any thing else.

UR PHONE COULD BE LOCKED UP BY UR SERVICE PROVIDER OR UR SIM IS DAMAGED