How many unique three-digit extensions can be assigned using the digits 2 through 9?

The numbers 2 through 9 on a telephone keypad, like the one shown, are associated with the letters of the alphabet. Each person in a particular office is assigned a phone extension based on the first three letters of his or her last name. For instance, John DOE has the extension 363, and Marvella JOHnson has the extension 564. How many unique three-digit extensions can be assigned using the digits 2 through 9?