Starting in the 1970s, pay telephones were less and less commonly placed in booths in the United States. In many cities where they were once common, telephone booths have now been almost completely replaced by non-enclosed pay phones. In the United States, this replacement was caused, at least in part, by an attempt to make the pay telephones more accessible to disabled people. However, in the United Kingdom, telephones remained in booths more often than the non-enclosed setup. Although still fairly common, the number of phone boxes has declined sharply in Britain since the late 1990s due to the boom of mobile phones.