
Originally Posted by
slomojojo
That's already built in. Once you choose "United States" in the address book, there are entries for "Armed Forces XXX" as states in the drop-down menu. You'd type in APO, FPO or DPO as the city.
Just be sure in the admin panel to choose the option to always offer the dropdown menu for the states.
You might want to customize the entries a little bit. You might change the default "STATE/PROVINCE" field to something like "CITY or APO/FPO" the way it is in the graphic you provided.