Format: 

[1]F. Lastname, private communication, Month Day, Year.

Examples: 

[1]J. Jones, private communication, Jan. 31, 2012.

[2]J. Doe, private communication, Nov. 14, 2010.

Notes: 

A personal communication can be private letters, memos, emails, interviews, telephone conversations, etc. Personal communications do not provide recoverable data and therefore limited information is required in your reference list.

Questions? Contact an RIT Librarian at libraryhelp@rit.edu

Source:
IEEE - Unpublished, p. 38