I just spoke with a 911-training director here in WA -- She said that, just like unsubscribed cell phones calling 911, unsubscribed land lines or wired or conventional telephones should also work to 911 (It's apparently a federal requirement).

Your cared-for person may need to make arrangements with the serving wire-line telephone company and there may be a one-time service charge to set up the service, but it seems it is possible to have 911 access from a home telephone instrument without having actual telephone service. Call the telephone company and don't take no for an answer.

A speaking person will have to make a 911 call, quickly identifying the call as a test, to verify that the phone company data base (to which 911 apparently gets access) is showing the correct address.

Apparently, there is no provision to register an address for a cell phone -- The telco provides the fixed address for wired phones and the cell phones are located by GPS (if the cell phone has it and it's working).