http://www.pokercoach.us/RobsPkrRules4.htm
ROBERT’S RULES OF POKER VERSION 4
SECTION 3 - GENERAL POKER RULES
THE SHOWDOWN
2. Cards speak (cards read for themselves). The dealer assists in reading hands, but players are responsible for holding onto their cards until the winner is declared. Although verbal declarations as to the contents of a hand are not binding, deliberately miscalling a hand with the intent of causing another player to discard a winning hand is unethical and may result in forfeiture of the pot. (For more information on miscalling a hand see “Section 11 - Lowball,” Rule 15 and Rule 16.)
but i would say it varies from house to house but most places play hand calls itself.