It used to be possible to work out a 3DS unlock key from the enquiry number using an algorithm. This is no longer possible, and now only Nintendo can match a key with an enquiry number.
*222*2#balance enquiry number
The enquiry number for Howrah Station is 139.
There is no such thing as a Nintendo 3DS master key. The key that can be used to reset parental locks, was at one time able to be calculated using the reference number the console generated for you. This is no longer possible, and there is no universal key that can bypass the need to contact Nintendo.
The numbers are underneath a scratchable layer, you scratch it off to reveal it, then enter the code.
*125# to get flash enquiry display within seconds
123
*111#
*222*2#
to register your friends your friend must have a 3ds with swapnote also and then once you find them you have to enter there code
no 3ds games are only for 3ds because it has a thing on the side that wont let it enter
A person can get their 5 number 3DS master key for their Nintendo 3DS by calling Nintendo direct. A person may also obtain the number through the parental controls setting on the device.