I had an interesting question from a customer today about wanting to add to the list of Emergency Numbers that you can dial when the device is locked.
Today that is limited to the various different international emergency numbers but the customer wanted to add their own emergency disaster recovery number to their devices.
I discovered various articles across the Internet including this great one on Modaco
In summary to do this you have to modify the registry key HKLM\Security\Ecall
It is currently set to the Values: "List"="911*112*08*999*"
You can't simply change the numbers by editing the values as you'll get an error message: "Unable to perform this operation". What you need to do is rename 'List' to 'ListX' then create a new Multi-String Value, type 'List'.
One of the challenges however is that the Security registry key can be a protected area on many devices so you may need to work with your mobile operator or OEM.