According to the "Publication Manual of the American Psychological Association" (6th edition, 2nd printing), you must give credit to the source any time you quote, paraphrase or summarize another person's words or ideas. The format for parenthetical citations and the Reference page varies from the typical structure when using a source such as a memorandum.
Since they are considered unrecoverable information, unlike books and articles, personal communications are not part of the References page in APA style. The point of the References list is to allow your reader to find the original source in order to learn more about the ideas you have presented. Because a reader is unlikely to be able to find a memo, you should instead give the bulk of the information about the memorandum in the body of the paper, just as you would for a personal letter.
The citation in APA style typically includes the author's last name and a year of publication, but personal communications differ. The in-text citation therefore includes the author's first initial and last name in normal order along with a notation indicating "personal communication" (without the quotation marks) and a specific date in month-day-year order. Commas appear after the author's last name, after "personal communication" and between the day and year. For example: (J. Smith, personal communication, March 31, 2013).