If the box is still in use (50+ calls made in the last year) then it's kept. If it's in an area with low mobile coverage it'll be converted to a free wi-fi hotspot. Otherwise it's free to be torn down or used by the community (they show a box being used as a tiny library).
Clearly these relics have a point, as outlined by the article, but is likely that few (if any) are cost effective from a business perspective. Defining what constitutes their purpose from a social perspective is certainly valid for determining when they should be maintained.
It is all too easy to forget that there are people lead different lives from us. Some people don't have access to phones, or may need to use a phone where their calls cannot be traced by people who are close to them. Children are cited, but even adults in an abusive situations should count. While accidents are cited, there are also victims of crime (e.g. someone who was mugged late at night). Even those who own a mobile phone for emergencies or employment purposes may need to use phone booths, since a long distance calling card and a quarter for a local call is cheaper than a plan with comparable "free" local minutes (or it was about 10 years ago).
