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. Many locations that provide pay-phones mount the phones on kiosks rather than in booths—this relative lack of privacy and comfort discourages lengthy calls in high-demand areas such as airports. Special equipment installed in some telephone booths allows a caller to use a computer, a portable fax machine, or a telecommunications device for the deaf. Privacy Phone booths have been subject to wireless surveillance by law enforcement. For example, the landmark U.S. Supreme Court case of Katz v. United States involved the Constitutional question of whether the Federal Bureau of Investigation (FBI) could install a listening device outside of the booth. Paying for the call Coins The user of the booth pays for the call by depositing coins into a slot on the telephone. With some telephones the deposit is made before making the call, and the coins are returned if the call attempt is unsuccessful (busy, no answer, etc.). With other types of telephone coins are not deposited until the call has been made and the caller hears their party answer. The deposit of coins then permits two-way conversation to proceed. Cards Calls may be paid for by entering a payment code on the telephone's keypad, by swipe-card ("Swipe & Call") or by using a telephone card. Some pay phones are equipped with a card reader that allows a caller to make payment with a credit card. Collect call A caller who possesses no means of payment may have the phone company's operator ask the call recipient if the recipient is willing to make payment for the call; this is known as "reversing the charges", "reverse charged call" or a "collect call". It is also sometimes possible to place a call to a phone booth if the intended recipient is known to be waiting at the booth, but not all phone booths allow such incoming calls. Long before "computer hacking" was a common phenomenon, creative mischief-makers devised tactics for obtaining free phone usage