Personal comunications include conversations, letters, interviews, e-mails and telephone conversations.
• IEEE style states that you cite only published works, forthcoming published works, and unpublished materials available to scholars in a library, a depository, or an archive.
• For interviews or other "non-recoverable" information, no citation number is necessary.
This does not mean that an attempt to identify the author is unnecessary, but that it needs to be done in the text itself:
"In a personal interview with Bill Gates, he suggested that he would soon rule the world."
"In a letter to the author, Professor Mueller detailed his expereinnces with using this data collection software."