Hello Jim,

You can try this one:
IF((LEN(TRIM([Firstname]))=1) OR (LEN(TRIM([Firstname]))=3 AND POS(TRIM([Firstname])," ",2)=2) , "Friend, ",[Firstname])

Instead of trying to check all of possible 2 letters combination you can have, this function checks if it has a space in between the 3 characters found or if it has only 1 character.

Hope this helps!

Edited by JFLAIR (04/01/16 04:49 PM)
Edit Reason: Added a TRIM()