Area code 664 in a telephone area code in the North American Numbering Plan (NANP) for Montserrat, a British Overseas Territory in the Caribbean. The digits of the area code translate to MNI in the alphanumeric mapping on telephone dials. The area code was created in a split of area code 809, with a permissive dialing period from 1 July 1996 to 1 June 1997.

A local call within Montserrat is dialed with seven digits. A call from another North American Numbering Plan country (such as the United States or Canada) requires dialing the long-distance access code (1), the NPA code, and the seven-digit telephone number.

At one time the small island of Montserrat used only four-digit telephone numbers internally, as the first three digits after the former 809 area code were the same for everyone (491). As of May 2011, Montserrat has seven-digit numbers beginning with 236, 349, 410, 411, 412, 413, 415, 491, 492, 493, 494, 495, 496, 664, and 724.