FYI versus an FYI, versus a FYI

[Unregistered]

What is correct - FYI, or an FYI, or a FYI? If this is 'an FYI', is it because of word Information - "For Your Information"?

[florr0]

If FYI is used as a noun is must be 'an FYI' because the 'F' has a vowel sound (ef)

[Anglika]

What is correct - FYI, or an FYI, or a FYI? If this is 'an FYI', is it because of word Information - "For Your Information"?

If you are using it in a letter/e-mail, just FYI. No article is required.

[Barb_D]

It's commonly used as a noun though.

Jim, Anne: Please review and let me know about your edits.
Pete: This is an FYI only - no action required.

You're right that we could write it as "Pete: This is FYI only" but it's showing up quite a bit as a nou anyway.