If you forgot your phone lock code or bought the N900 second-hand and can't seem to locate the seller to ask for the phone lock code. You can now get the phone lock code quickly without sending your phone to a service center.
Before you can follow the instructions below, you will need to access the N900's terminal shall and be able to access root privileges. This can be done by running the Application Manager and installing an application called "rootsh".
You will also need a tool on your computer (I assume you are using Ubuntu) called "John the Ripper", go to a terminal shell and type:
$ sudo apt-get install -y john
On your N900, go to the terminal shell and type in the following:
$ sudo gainroot
# echo root:$(grep -A 13 lock_code /dev/mtd1|tail -1): > /home/user/MyDocs/phone_lock_hash
This will create a file called "phone_lock_hash" at path /home/user/MyDocs which you will need to transfer to your Ubuntu computer where "John the Ripper" is installed. The easiest way to transfer the file is to use the USB cable provided and plug the N900 to your computer in "Mass storage mode". You will find the file "phone_lock_hash" in the "Nokia N900" storage device.
Once you've copied the file, you can then start brute forcing the password. Again, go into a terminal shell and type:
$ john -i:digits phone_lock_hash
Depending on the length of the password and the speed of the processor used, it can take anywhere from a split second to a few hours to crack the hash. The "-i:digits" tells the tool to only use numerical digits since the phone only accepts numerical input for the password (this speeds up the brute force process).