I'm not sure what you mean by locked/unlocked as those terms are applied in different places. The phone can be "locked" with a password. Then I gather that the phones can be or are locked/unlocked to carriers (I've verizon so I don't know this issue) and further the sim card aspect can be locked/unlocked (this is a verizon 8830 issue).
But it appears that the Garmin 5 version uses DATA to get the maps and probably the routing. It also has access to weather and traffic and uses data for that obviously.
There is/was a Garmin product that apparently stored the maps on an SD card and probably did not need DATA.
I think this product is for the lifetime of your device - that is change device and you probably lose your registration but I don't know for sure.