catymag
GarminDevice.xml is recreated each time the device starts. The firmware never reads from it but only writes to it.
Giomen
Don't confuse people, RAM doesn't store data permanently. It is non-volatile memory which store data permanently, also there are a few more flash regions that can do it.
Why are you so sure that phone book, etc. isn't stored in the filesystem? Did you check all the .db files which are just SQLite databases? Security is a bad argument, as firmware can encrypt any data on the filesystem. non-volatile memory isn't secure also, as we can easily read it, write it and decrypt it.